Find a critique of the philosopher's ideas, written by another philosopher who can explain them.

SEP is a gold mine. Free to access peer reviewed philosophy encyclopedia. The hyperlinked text in this post takes you to an article titled "Aristotle's Metaphysics".

A similar site IEP exists, and that link is to its article on Aristotle's metaphysics.

there's also a mountain of secondary material on Aristotle's Metaphysics -almost too much, actually, in the case of this particular text, which is arguably one of the two or three most influential texts in the history of philosophy.

But, in addition to secondary texts, there is nowadays a wealth of online learning material and published university courses - here, for example.

I've noticed a contemporary scholar called Joe Sachs whose translations seem well-regarded, although I can't vouch for them personally. https://www.amazon.com/Aristotles-Metaphysics-Aristotle/dp/1888009039

I suggest learning a little bit of Greek.
Aristotle repeats many words and phrases. When you see how the translators are arguing for how to understand those words, the world suddenly gets smaller.

When faced with canonical works such as Aristotle's Metaphysics, I generally turn to the secondary literature for help. Fortunately, in this day and age, it is easy to find most of this literature for download on the internet if you know where to look...

Now, generally the secondary literature itself may be a mess, so how to navigate it? If you're completely new to the subject and would just like an entry point, one good beginning is to look at SEP and IEP, already linked by . Another is to search for guidebooks and authoritative translations. In the case of the Metaphysics, for example, there is a guidebook by Vasilis Politis in the Routledge Guidebook series that seems fair enough for a beginner, and there is also a recent translation of the book (with many, many notes; in fact, there are more pages of notes than of the text itself!) by C. D. C. Reeve (you can read a friendly review here).

After this, well, it depends on your interests. If you are puzzled by specific books, you may either consult the translation of those books in Clarendon's Aristotle series, which tend to be excellent; and, if you are lucky, there may also be volumes of the Symposium Aristotelicum dedicated to it (I know for certain that there are volumes dedicated to Alpha, Beta, and Lambda, which are all excellent). From there, you may try reading the more specialized literature, which has mostly concentrated on Zeta. Classics here are G. E. L. Owen's articles "Logic and Metaphysics in Some Earlier Works of Aristotle" and "The Platonism of Aristotle" (Owen was a detestable man, but those articles are indeed important...), Michael Wedin's Aristotle's Theory of Substance, and, more broadly, David Charles's Aristotle on Meaning and Essence.

In my own case, I'm particularly interested in the relation of the Metaphysics to Aristotle's biological works, such as the History of Animals, the Parts of Animals, and the Generation of Animals, in the tradition of David Balme and his students. So I particularly like Montgomery Furth's Substance, Form, and Psyche, which approaches Aristotle's works through that lens.

For exemple, currently I am reading Metaphysics by Aristotle (from beginning to end). It is really hard to understand. I feel like I'm stuck. I am reading with two different translation.

When you face difficult books what do you do? You keep reading even without understand? What can help in this situation? — John Pingo

Find something that is easier to read, something more meaningful to you. Reading without understanding is pointless.

1) Don’t use commentaries by other philosophers.
2) Read a paragraph and think.
3) when you’ve finished a section write a summary of what you’ve just read - helps to improve retention.
4) Take a break and/or read something by a different author on a related subject.

Once you’ve got your own idea about the text (or failed to understand) then look at other philosophers commentaries on the text.

As you build a broader knowledge you’ll learn to understand better.

Simply put, persist. Reading is a skill that takes a lot of effort and hard work to improve. Reading words isn’t really reading. You can practice by reading a couple of pages of a novel closing the book and then giving a detailed summary in writing.

GL and work hard :)

When you face difficult books what do you do? You keep reading even without understand? What can help in this situation? — John Pingo

In my opinion, if you find serious difficulties in understanding a book on philosophy, don't waste your time. Leave it. This is my main advice.

If you want to learn math, don't start with elliptical equations in partial derivatives -whatever the hell this means.
If you want to learn philosophy, start with simple texts for popularization or teaching. They wouldn't be the non plus ultra of philosophy but they help.
In general, great philosophers' books are difficult to understand because they pose complex problems, use particular jargon or because they are written in the past, in a language that is no longer ours.

However, it is possible that even if you do not understand the text, you may find some ideas that interest you. This is often the case with me. For example I'm not sure I understand exactly what Sartre says in Being and Nothingness, but I find that reading it enlightens me about certain aspects of my life. Perhaps it is worthwhile then to continue reading slowly and without getting impatient. This is like reading poetry. You seem to understand it, but maybe not.

These are two ways of reading philosophy. Both are productive for me.

I don't advise you to read Aristotle if you have not a previous knowledge of Ancient Greece and its culture.