There are several websites available that can instruct you on poker. I made an effort to learn from each of them, including Cardschat, Twitch streaming and YouTube videos. I can tell you one thing, though just like learning to play chess, understanding the rules is one thing, mastering the game is quite another.
If you have never played Texas Hold'em before, searching for its rules on Google would be the best place to start. Download the
pokerstars client,
register for a free account and play a few play-money games to gain a feel for the game, in my opinion. Even while free games are very different
from paid ones, you will at least gradually adapt to how things operate at the tables.