1) Standard memory is what shipped with your laptop from the factory which in this case appears to be 2GB. You appear to have one empty memory slot. The built-in memory in your laptop is replacable if you wanted to have the maximum 8GB (2x4GB) of memory installed.
2) The link you have in your post shows the Crucial recommended memory for your laptop. If you order a module from your link Crucial will guarantee compatibility. (I believe it has 204 pins)
3) You "can" buy any RAM you want, but be careful to at least buy a name brand or you will likely have issues. Buying the least expensive no brand memory is usually a recipe for disaster. Crucial has one of the easiest websites to identify compatible memory for your system with guaranteed compatibility and I have found it is very rare to receive a defective module from Crucial. I have personally found Crucial to have affordable & reliable memory with an easy to use website & helpful customer support.