Can I mix RAM cards?

[ImOnly15]

(I'm only 15 years old and i'm not a computer wiz so please bear with me) Ok, so i have this old 4GB ram card from an old Toshiba laptop (I don't know what model) I've recently gotten a new Dell Inspiron 14z laptop, it has 2 slots for RAM and the RAM cards are 2GB each. I decided that i would replace one of them with the Toshiba RAM and i put it in, and pressed the power button on my laptop. It started as it normally would and everything is working as normal. I'm just wondering if what i've done will have a bad effect or a good effect? Like i said i'm not good with computers.

 

[basroil]

1) If you're lucky the machine will run in flex mode, running 2+2 in dual channel (faster memory) mode and the remaining 2GB in single channel. If you're unlucky it will slow down the memory speed by half!
2) As long as both use the same memory speed and voltage (probably DDR3 1333MHz sodimm 1.5V), it should work without damage