Here are some useful questions you can in English ask when you join a gym.
Asking about membership options
Can you tell me about...
I'd like some information about...
Do you have any special introductory packages?
What sort of membership options do you have?
How often can I use the gym with this membership?
Asking about cost
How much does a weekly / monthly membership cost?
How much would it cost to pay each time I use the gym?
Saying what your interests are
I'd like to lose weight / get fit / tone up / build stamina / increase muscle strength
What do you suggest for... (weight loss / weight training)?
Asking about classes
Do you run any classes?
How many times a week is there a kick-boxing session?
Is there a waiting list for...
Do I need a medical certificate for these classes?
Asking about the facilities
What sort of facilities do you have?
Can you show me how to use the equipment?
When's the quietest time to come in and use the gym?
How late do you stay open?
Are you open at the weekend as well?