Newby_when I need to pay the first months?

Hi,

I began working as a freelance in UK during December 2014, and I registered for the online self assestment around mid February. Currently I am working full time as a concept artist, and freelancing as an illustrator for a big company the rest of the time. I am not sure, according to my situation, when I need to provide the self assestment and pay my taxes, before the next 31 th January 2016? For which period I will be paying then, for the 2014/15, so in my case I would need to pay my activity during December 2014, January, February, and March 2015?

Sorry, but I am neither experienced freelanced nor native in English, so I need a bit of help to begin, I don't want to receive any fine for not paying the correct amount during the correct period, and also I don't want to pay more than I should.

Thank you!