So I know already about the command tense where in the sen form you say for example gel or gelme. 

However I´ve come across a third person form where one would say gelmeyin/gelin or kullanmayın/kullanın.  

Is this the same tense but just the o form? 

It´s a different tense but very similar in meaning - just a more formal or polite way of giving instructions:

http://www.turkishlanguage.co.uk/imperative.htm

You can also use -iniz as a third even more polite form. So in Turkish you have:

Bak

Bakın

Bakınız

Thank you so much this helps a lot!