Is the Sicilian Defense a good opening for beginners? Just discovered the chess section of this website. This is my first question here. 
I am a beginner chess player(rated about 1300 on the chess websites) and play mainly for recreation. For a long time, my opening repertoire was restricted to 1) e4 .. e5 . 

However, while playing black I get tired with the fact that white is always calling the shots, and also bored of playing the same lines. I've tried the french but find it a bit predictable for the white player and with less variety. 

I would like to try the sicilian. I know that this is often preferred by grandmasters. However, the grandmasters typically gain the advantage only in the end game. However, the style of grandmaster play is quite different from the style of beginner/amateur play. Grandmasters would often go into the end game with no advantages of material. By contrast, in beginner/amateur play often the better player gains advantage in the middle game itself and by the time he reaches the end game he is already ahead in material by a rook or a bishop. Keeping in mind this difference is the sicilian a good opening for a beginner? Or is it more for the more advanced players and end game specialists?
Also, how to play it correctly? I've tried playing it a few times but am yet to understand the underlying principle. Which is the better second move -  2) .. e6 or 2) .. d6 ? Why is the rook pawn sometimes advanced prematurely ( 4) .. a6  or 3) .. a6) ? ... etc., etc.
The Sicilian is playable at all levels. 1.e4 e5 openings are easier to understand, so you will often see 1...e5 recommended for beginning and intermediate players (and I second that recommendation), but there's nothing wrong with 1...c5, and you should feel free to try it out and see if you like it.

To say how to play it correctly would take hundreds of pages. To answer your two specific questions:


After 1.e4 c5 2.Nf3, 2...e6 and 2...d6 are both perfectly good moves played at the highest levels.
The move ...a6 in the Sicilian has a few points, but the most important are that 1) it can keep a White knight away from b5, and 2) it can support ...b5 and start a queenside attack.