u/Hjull

For context, my grandparents sent me $10,000. They want me to either put it in retirement or invest it. I'm 21 and just finished my third year of my undergrad. I don't have any debt so nothing to pay off. I have about $400 in a retirement account and about $7,000 in an investment account.
My questions: Do I invest it all? Do I put it all into retirement? Do I put half in each? Do I split it in some way into each?

I recently left a job where I had a 403b retirement account. Where should I rollover what I have? What difference is there between a rollover IRA or a traditional/roth IRA?