Specialist waxer here lol !
Ask for HOT WAX if they have it and even if it is slightly more expensive, it’s worth it
First you would need to remove your clothes ideally from the waist down (undies included) and lay on the bed with a soak towel covering your modesty until your therapist comes in to commence the wax.
Then you should put both legs bent (think frog legs) and hold your stomach / top of pubic area tight as it helps keep the skin taught when we remove the wax.
Deep breath as much as you can and try to talk to the therapist if you can as it does help. And remember its only a quick pain and usually treatment is done within 15/20 mins.
Also have your crack (bum hole) done - we’ve seen it so many times and honestly the wax will feel ‘incomplete’ without the whole area cleaned up. And you won’t realise how much hair is back there until you have it waxed 
After the wax you may feel about sore and abit sticky - it’s normal and the redness and sensitivity usually goes down within 24 hours. For the first 48 hours after the first wax I would suggest avoiding sex, exercise, tight clothes, swimming, hot baths, scented perfumed prouducts and and any sort of heat treatments (sun beds or sun bathing) as the skin could possibly react although it’s very rare.
Also after the first week after waxing start to exfoliate twice a week using an exfoliation glove as the body scrubs aren’t usually abrasive enough - to avoid getting ingrown hairs.
Your next wax should be due in 4-6 weeks although you may experience some hairs growing sooner especially after your first wax as hairs are sometimes at different stages of the growth cycle but continue to wax and it does regulate and you will notice a smoother finish after each wax.