I am a student and I would like to offer my translation services online. Can you suggest me some tips to manage my time between the two tasks?

Speaking from eperience, be realistic with the time you offer. Do it on the time you make free but always keep your school work first. Manage your time well and you should not have a problem in doing this. Its more about choosing the priorities and your services so that they do not over lap each other.   

.You can join any company and offer your abilities to translate movies or songs

I believe it would be better if you can employ the second task to serve the first!