How to know which memory RAM I can use on my laptop?

I've been needing to buy a new memory RAM for my laptop, but as I'm new on this type of things, and from the Internet I found out it can't be any random memory RAM, I am not sure which memory RAM I need to buy so it will work on my laptop.

I know that my actual RAM says this:
4GB 2Rx8 PC3-10600S-09-10-F2 (DDR3)

I've tried to find that memory RAM on google but it was unavailable, creating the need of searching for a new one.

I've heard crosair is a good one about memory RAM's, but I don't know which ones are compatible with my computer, which one will let my computer boot if I place it there.

I know that it needs to be DDR3, and need to have "PC3-10600" which I don't yet know what it is. On the task manager it says the RAM is 1333Mhz. Which would lead me to:

1333Mhz
PC3-10600
DDR3
Either 4GB or 2GB

There is also something about voltage, but how do I see which one I need to have? I found out a RAM which is:

SODimm DDR3 4GB Corsair CL9 1333Mhz and 2GB version

Yet I get no more information from the website that's selling (I am buying from portuguese websites due to Portugal being where I live)

I kinda need help about what should I know and look for when buying a new RAM for my laptop.

Answer

As long as the RAM is DDR3 and 1333MHz, you'll be fine. It's always best to find the same brand, but that isn't the most important thing.