You carry out a process called 'binding' to ensure each 2.4GHz DSS transmitter only talks to the correct receiver.

You will not require a licence from OfCom in order to use your 2.4GHz DSS transmitter. 2.4GHz is in the Industrial Scientific & Medical (ISM) band which is licence free.

Nothing wrong with questions, but check to see if they've been asked before using the search function. There's a lot of answers to the common questions on these forums.

Hope that helps!