Can you play all sims3 games at once?

the game works like this for example i haave the sims 3 , pets, world adventures and seasons i install the sims 3 first as that is known as the base game, then i install pets world adventures and seasons since seasons is the last one i install my game will play from the seasons game but all the other games and items are installed too

Yes, you can play the game, there are expansion that connect with each other

What azraeilamon and rumbutter said is absolutely true. To give you an idea how that would look like in your launcher take a look at this screenshot:

At the bottom of the launcher you see little symbols for the base game and all expansions and stuff packs (I marked them in red for you). All the symbols that are high-lighted are expansions or stuff packs that you have installed. All the symbols that are greyed out are expansions or stuff packs that you don't have installed. When you hover with your mouse over one of the little symbols you'll get a text box that explains which expansion or stuff pack the symbol represents.

When you start the game you will have access to every feature and design that came with the expansions and stuff packs you own. The easiest way to see that is in Create-a-Sim (CAS) or Buy Mode. The little symbols for the expansions and stuff packs will show up there too: