Mate explaining one by one step is really difficult from here. But however I am sure that Google have added videos so that a new person like you can understand easily. Just search for the official channels of adwords in you tube.

G will show your ads for keywords you have not bid on if G decides they are related terms. The only way to stop this is to put your keywords in quotation marks or [ ]. You can also go through your logs for the terms Google is broad matching and use the negative keyword tool to take them out one by one.