The first betting round in Texas Holdem takes place immediately after splitting the cards to the players. The first player is the one placed in the left side of the dealer, as he has to place the Big Blind. Once this player has placed the respective bet, he also has the right to raise the stake. For the special tournaments, there is a possibility for the players to place the third Blind, which is called Straddle. The advantage of the player that places a Straddle is the one that, for the first betting round, he is the last one to place the bet, and this allows him or her to consider all the stakes that were previously placed.
The player that wants to Call in Texas Holdem has to place an equal stake with the Big Blind or with the Straddle. If you want to Raise, you will have to add an extra sum. Considering the type of games, you can only raise with a limited sum (those are the Limited games), or you can bet all-in, meaning that you will bet your entire budget on a single hand. Another player that has a smaller budget can place an all-in bet, but if a player that has a smaller budget than yours wants to call for your all-in, he will only need to place a bet equal to your sum.