RAM stands for Random Access Memory, this is memory that the computer can use to run programs while the computer is on, its kind of like short term memory. The more RAM you have doesn't necessarily mean that your computer will run faster, if a program only utilizes 2GB of RAM it doesn't matter if you have 4GB or 32GB.

*note that RAM cards can be alone or paired, two cards can work together to double the RAM, like 2 4GB RAM cards will provide 8GB of RAM, if you want two RAM cards order two of that amount of gigabytes, not one of the sum you want.

2GB of RAM is, well, not very good, you can't run too much with it and you'll have a very slow computer.

4GB of RAM works, it'll have some lag, and difficulty running large programs or complex games.

8GB of RAM is what I would recommend for a good home/work computer. If you have a good cpu too, you won't experience much lag at all and it can run most programs.

32GB of RAM is a lot of RAM, it will make a really powerful gaming computer and can run any game or program short of Artificial Intelligence.

64GB of RAM is more than I would know what to do with. This would be an incredibly powerful computer.