Plugins in Multisite

Ok, so I am probably starting from the off on the back foot here, but here goes. I am seriously confused with regards to Plugins in general. When I download them and, "Network Activate" some seem to appear across all sites depending on the plugin. I have tried to find the answers online however I'm either really stupid or can't find it.
I would like to be able to download plugins and chose which ones will be network wide and which ones will appear on a single site? As an example, I installed WP-Store for a new clients site, and its fine until I noticed it showing up on a different clients site which is not very helpful. It is also confusing that it does not show on the Network Admin section.

I found this article and probably should mention that on my installation I do not have the option of installing as per the image, "Activate"..."Network Activate", I have "Activate" thats it. Don't know if the article is out of date.

To make it easier can you tell me how to simply download plugins and to be able to activate say for example the Events+ on the entire network or only on a couple of sites.

Thanking you in advance,