Note: For much more detail on installing memory (and all your other parts) including quality images from our most recent real-life build to make it easier for you to follow along, check out our complete How to Build a Gaming PC in 2017 guide.
Installing your RAM modules is typically one of the easiest and quickest PC components to install when building a computer. It's also easy to do when upgrading the RAM of an existing system instead, which is essentially the same process as installing RAM into a fresh new build.
Just one note on upgrading - if you're installing RAM into a pre-built desktop PC that you bought, I would double check to see that adding new/more RAM into it won't void the warranty.
Ok, firstly you need to locate the memory modules on your motherboard, and figure out which modules you need to install the RAM into as some motherboards will require you to install them into specific modules (and using the wrong modules won't work). For example, if you're installing 2 sticks and are running dual channel memory, you want to find out exactly which 2 motherboard slots you need to install them into.
Refer to your motherboard manual to be sure you use the correct motherboard RAM slots.
Now you can remove your RAM module/s from the anti-static bag they should have come in. Memory isn't the most delicate of hardware parts, but still try to only handle it by its edges and avoid touching any bits that look like circuitry etc.
Now to actually install the RAM, you simple line it up with the correct memory bank and slide it in carefully until it is secure. Some motherboards will have little clamps on either side of the motherboard's RAM slot that you need to push down to fully secure the RAM in place (and that may need to be unlocked to begin with).
Note that this is how you install DIMM RAM. If you're installing SIMM you will need to place the RAM into the memory bank slot at a slight 45 degree angle, and push it forward until it's perpendicular to your motherboard.
That's basically all there is to installing RAM. The confusing bit may be finding the correct motherboard slots to install them in the right order when using multiple modules and/or multiple channels such as dual-channel memory.