how do I get details on performing maintenance on a briggs & stratton engine on a tiller?

Small engine repair school…. JK
The basics of Maintenance is:
Change the Oil, spark plug, and air filter once a year,
Some of this depends on how often you use it since there usually isn’t an hour meter this is probably best.
Drain the gass before putting it up for winter.
Hose it down and let it dry after every use.
Every three to five (depending on use)years change the contacts and (if it has it) the oil in the differential (s)
On a side note I’d also use a table spoon of keroseen to each gallon of gass and let that run through once a year. It will smoke bad but it cleans the carburator.

If you examine the engine you will find an ID placard from B&S some where. Write down the model and serial number and then go to http://www.briggsandstratton.com . They have owner and parts manuals for most of their engines available for download plus a troubleshooting assistance section.