Initial delay-That is after this many secs start putting load on system
Start-up time –Example if we have start thread count as 10 and we put this value as 10 as well 1 user will be put every 1 sec.
If we put it to be 20 ,1 user will be put every 20 sec.
Hold time- For how many secs all users will stay on the server
Shut down -How much time it must take for users to leave the site.Like if we take shutdown time to 30 secs then in 30 secs time all users should be removed from the site.i.e dont remove them all at once but remove the in some time.
IMP-We can even add a new row and define total number of users and everything in it.