For josaa counseling first login in to the portal page. Then choose the order of your listing the colleges according to your priority list and according to your rank. Then lock your choices. After each round either you will be alloted a seat or not alloted. If you are alloted a seat want to take it go to the institute and take admission otherwise keep floating your choice 

Dear Student,

The counselling of JoSAA is conducted for all qualified candidates to provide admissions into IITs, IIITs, NITs, and GFTIs as per their individual eligibility. You can check the complete process of JoSAA counselling in the following link of Careers 360: https://engineering.careers360.com/articles/josaa-counselling and you can prepare for the counselling by knowing about the frequently asked questions in the following link of Careers 360 : https://engineering.careers360.com/articles/josaa-faqs.

I hope this helps!