What do you do with Mark 16?
Well, first, you need to read it.
And secondly, recognize it for what it is. The so-called "longer ending" of Mark (v.9-20) has typically been considered by scholars and historians to be added later. It was probably added as extra material became available and more explanation was needed. It might have even been post-scripted in as a side note.
When something like that happens, folks who are hand copying the text don't know necessarily whether it's original or whether it's added or whether they should copy it or not. So some of our existing copies of Mark have the longer ending and some don't. When the King James Version of the Bible was published in 1611, it included it. So that's why it's in most modern day Bibles, even though it's noted in brackets.
The other side of recognizing it for what it is means that you realize that nothing that was said in the extra verses is contradictory to anything else in the Bible. In fact, it fits in quite nicely.
And besides that, the resurrection account in 16.1-8 is pointed and emphatic. Jesus is risen. Easter happened. And that news changes everything.