Anyone here a fish/tank expert?

[TheRandomHybrid]

I need more information to advise you.

How large is your tank?
How many guppies do you have?
Do you have any other fish/snails in the tank?
How often and what do you feed?
How often and how much do you clean?
What is your lighting schedule?
How long has your tank been set up?
Do the fish show any symptoms before dying - getting fatter, very thin, fins torn up/with white edges, white spots, swimming weird, sitting on the bottom, gasping at the top?

With this information, a true course of action can be suggested.

It's ah, I think a ten gallon tank
I currently have two
No
Flake food twice or three times a day
Once a week, most of the tank
7:30 am to 8:00 pm
At least two years
Mostly sitting on the bottom is what I notice the most. Could also be getting fatter.

[wepuddy]

At your locle pet store get a thing called test strips they uselly come in as bottle and you can test your water

[Bad Habit]

Well, first, cut back on the feedings. Once a day, as much as they can eat in 5mins. Also, don't change more than about a quarter of the tank at once, too much and you're doing more harm than good - you'll damage the beneficial bacteria in your tank. If your tank is heated, make sure it's between 79f and 82f.

If you think the fish are getting fatter before dying then it could be either overfeeding, or it could be something called dropsy. Look down from the top on your fish, and you might see something called pine-coning - their scales actually start popping away from their body due to internal bloating. If that is the case, you can treat dropsy by disolving a teaspoon of epsom salts into a small container of tank water and dumping it back in.

[TheRandomHybrid]

Ok. Thank you for your advice

[Eevn665]

Yes, as someone stated, is it cycled? The big question. It really does make a difference. Also, a bit of aquariam salt (not marine salt) can keep them healthy.
Also, with a 10 gallon, you can fit 5 or 6 guppies. Be sure to acclimate and introduce slowly, but only after you figured out what happened.