I need to fix my mower?

Hiya. I have a briggs & stratton 35 Classic (also on the front is written Trojan 18) that i was recently given from a member of my family. I have managed to get it started after alot of sweating but the problem is it is bellowing out white smoke and alot of it, even after the choke has been taken off. i initially thought it might have been something that would wear off after running it but it hasnt done so. I have the correct fuel in as well. I could really do with some help as i do not have the money to get the mower serviced especially if its something i can fix eventually myself. Any ideas would br greatly appreciated.