Use the adverb successfully to describe something that ends up having the outcome you desired. If you successfully snowboard down a mountain without falling, it means you've achieved something you set out to do.
If you attempt something and achieve it, you've done it successfully. You could successfully finish a term paper in time to have your friend proofread it, or successfully decorate your brother's birthday cake to look like the Empire State Building. When it comes out well, it's been done successfully. Spelling successfully can be tricky; it can be helpful to remember that there are two c's, two s's, and two l's.