You said "like I'm five " so I'll take you at your word and add a little detail. All spas are a little different but this how it is at my favourite day spa.
Arrive- reception will ask for your precompleted health questionnaire or fill it in with you. Asks about any health concerns, skin problems, pregnancy etc. Some responses lead to advice not to use some facilities. Get given a towel and robe.
Head to changing room to put on swim suit. This spa is separate men / women rooms and mostly open plan with a few curtained off private cublicles. Showers available. Personal stuff in lockers
Wearing swimsuit & flip flops and the robe they gave me, carrying a towel walk through to spa area.
There's 8 different rooms with different experiences . A sign suggests which order to try them in (working from least hot to most hot). Example: steam room, sauna, aromatherapy room, ice shower (!).
If the room has a door please close it quickly to keep the heat in . Doorway dithering is frowned on.
There are water dispensers everywhere: keep drinking little and often.
After going round I might spend half an hour on the sunbed by the pool then have a swim or hottub.
Lunch. Some people dress. Others stay in their bathers & robe.
Might have a treatment next. Facials and massage are lovely but any oils might limit what you can do after.
Back to the saunas and steam rooms. A sleep? An exercise class (all v beginner friendly).