you mean how can you sell items on your inventory?
•if you have a town•
→ go to gen.store/tailor/gunsmith bldg.
→ open one of the shops..
→ drag the items from your inventory to the left...*for sum its double clicking...*
•if you are not a town member•
go to the nearest town and do those above^^
if i miss sumthing feel free to add