They will need to come to your house. They usually ask that all interested parties be present, as there are many decisions to be made when considering a conservatory.
They will then establish the feasibility of the project and make some basic notes and drawings. You should ask to see photographs. Ask them to tell you all about their company and any independent accreditations they hold. Also ask about their guarantees.
Many of the major companies will then, subject to survey, be able to give you an accurate conservatory quote there and then.
This can be a good time to see what, if any, special offers they are running at that time.
You should allow a reasonable amount of time to be with the initial surveyor, as there is a vast difference between products available with which to build conservatories, and you need to know what you are buying.
Most companies will offer you a 
