what to do after getting provisional allotment letter from JOSAA
Depends if you're happy with your allotted college or if you want to wait till the counselling process gets over. If you're happy with the college you are allotteed then you need visit your nearest centre and get an admission slip for that college and you won't be able to sit for the next rounds once you do that. My suggestion would be to wait until the entire process gets over and then visit and follow up with the rest of the process.
Hope this helps :)