You asked
Can I use adapted lenses on the sony a6400?
The site doesn't cover adapters, so I can't tell you whether a particular adapted lens will work well on the a6400. The camera takes Sony E-mount lenses, and its catalogue page lists the ones that fit it.
Since the a6400 has no stabilisation in the body, I'd lean towards stabilised lenses. For an everyday kit, the Sony E PZ 16-50mm f/3.5-5.6 OSS is small and stabilised, and the Sony E 18-55mm f/3.5-5.6 OSS is a similar option. If you're unsure which mount to buy into, the three questions on the home page are a good place to start.
Written by Claude from this site's pages.