Asking advice in the Benoni

I had never tried the Benoni, and my first attempt didn´t go well. Early in the game my d6 pawn was under pressure, how could I have prevented the maneuver Nf3-d2-c4, combined with Bf4 and Nc3-e4?

You should try chasing away (or exchanging if possible) white's dark squared bishop with Nh5 before white's knight gets to c4. Otherwise, you may have to play Ne8 as in the game and will assume a passive position.

Also you typically don't ever want to allow White to play a5 -- after Black's ...a6 if White responds a4, you play ...b6 if possible, then possibly prepare ...b5 with ...Rb8.  But if you let White play a5 without having played ...b6, when you play ...b5 he captures your b-pawn en passant

Try the snake Benoni, good alternative imo

Nice idea 7...a6, thanks!

Ignoring the d6 pawn with 9...b6 is quite good, but you must be well booked up- the resulting positions are very sharp.

Most of the times, Black plays 9...Ne8 followed by ...b6 and ...Ba6, to challenge the c4 knight. I do not feel that an early ...a6 solves Black's problems- it rather makes the ...b6 and ...Ba6 plan impossible to implement.

Sorry, but this as a general rule is simply wrong. Foregoing a4-a5 by playing b7-b6 is an option black has, more often than not he doesn't make use of it. Instead black plays either b7-b5 which results in mutual weaknesses on b2 and a6, or maneuvers a minor piece to the b5 square.

As far as the game is concerned: In all openings, and very much so in the Modern Benoni, it's highly important to respond to what white is doing and not just play your moves until you are forced to react.

Google search for "benoni 'a4 b6' -audi" (otherwise you get results that include those for cars!)

Firstly, I don't know what the point of your google search is. Of course the move b6 exists in the benoni. I should also add that entering "benoni" instead of "modern benoni" is further misleading. Of course in benoni types other than the modern this is a different matter, because 1. there usually is no b5 square to utilize and 2. there usually isn't much pressure on b2.

Secondly, I don't know who wrote those articles or made those audios, but regarding the information that a7-a6 a2-a4 should generally be answered by b7-b6 in the Modern Benoni, there are exactly two possibilities: You might have misunderstood what was taught, or the teacher was not qualified at least as far as this opening is concerned.

OK so maybe a4 shouldn't "generally be answered by b7-b6", but lots of times it should at least be considered, as just the sort of "pattern" that Silman has written about in his current article here on chess.com.  I'm not saying the articles from the Google search explicitly say to follow this, but they cite games where Black has answered a4 with ...b6, two of those right here on chess.com, one by Silman again, the other by Serper.  Much prior to all of this, I remember learning of this pattern when I was around 10 or 12 from Hartston's book on the Modern Benoni was then enjoying renewed popularity due to Fischer's employment of it against Spassky in 1972.  I could be wrong but don't believe I've misunderstood this, though I do appreciate you pointing out the possibility of Black exploiting the b4 square with a minor piece if White advances a5.

Yes, I've been a Modern Benoni player for about 20 years, and I often do consider it. It is an important pattern. In fact I recently talked about this subject with a friend, a rather strong GM whose main weapon against 1.d4 is also the Modern Benoni. We found that I generally have a liking for the b6 move and he doesn't, which probably has to do with me generally liking slow prophylactic chess while he is rather the for-the-throat kind of guy.

But if you look at a larger number of GM games and at contemporary opening theory, you will find that other patterns occur more often. a4-a5 b7-b5 axb6 and now taking back with either a heavy piece (pressure on b-file and protection of a6) or the d7-knight (monitor the c4 square and open square d7 for other pieces). Or Bd7-b5, or Nc7-b5. Sometimes these ideas can be combined.

Btw, looking for sequences of moves can be rather misleading. Take a look at the Silman article you mentioned, if I haven't missed anything only the game Brunner-Iordachescu shows the sequence a4 b6. But here the main point of b6 is not to prevent a4-a5 (white was certainly not intending to play this anytime soon), but to complete development (Bc8-b7) and put maximum pressure on d5, thereby preventing e4-e5. This is the slow setup that black can choose in the Nb4-line of the Taimanov. The alternative is to go for an early f7-f5, which leads to very sharp play.