You can play at more than one table when you are playing online poker. This is an option that is offered by every site individually, or you can choose to play at multiple sites at the same time. However keep in mind that poker playing software is different for each site and your computer might not take the challenge of running them all at the same time. You will have to try different software from different sites and see which ones work best for you. The last thing you want is to use many programs at the same time that will cause your computer to crash and you will lose money in games you cant even play until you restart the PC.
Once you have chosen the right software for you, then you can play at multiple tables in many different ways. You can change the tables manually, switch between them and see every time when it is your turn to bet, you can set up the software to let you know when it is your time to bet or you can adjust the size of every table window so you can see them all on your screen. It is better to see them all because you can see and compare others decisions and bets, but it is totally up to you and you will have to try playing in every way you an think of...