Getting confused with wallets...

Hi dear people,

I understood how to put btc on a platform for trading and getting it back on my computer wallet (electrum).
But I don't understand how to handle more than one wallet on one computer.

I cannot find in electrum or any other wallet software (how do you call these apps all together?) where to set which wallet you want to use, how to create a new one, and how to switch from one wallet to one another!

Right now I have a wallet, coded with paraphrase. Created with electrum.
I also have bitcoin-QT but I feel insecure about opening it and getting a mess because I don't know what would happen then. (Is the wallet from electrum gonna be switch to QT or automatically a new one created?)
At the same time I'd like to spread my little savings on 2 wallets instead of one...

How does this all work???
THANKS!!!!