Deniz,
Please read the stickies at the top of the newby forum, they are full of information to help you.
We need to know what filter you have and what your tank set-up is, along with water parameters and how long it has been running. Is your tank cycled??
Does your water company add Chlorine or ChlorAmine to the water - this will determine what you treat your water with. If it uses Chlorine then Stresscoat or similar will be ok but ChlorAmine will need something different, check on the bottle to find out what it neutralises.
Typical Maintenance Schedule for established tank (3months+) -
DAILY
Count fish and check all are active and healthy. Check water temperature. Check filter working. Feed Fish.
WEEKLY
Remove 25% of tank water, replace with conditioned water at same temperature, vacuum gravel while removing water. Remove yellowing leaves and any dead bits from plants. Clean front/sides of tank to remove algae. Check all fish are still there (not thrown out in water

)
Ensure filter flow is sufficient. Sit back and enjoy

MONTHLY
Test water, if filter flow reduced rinse media in tank water.
Andy16 Why are you recommending changing the filter media monthly?? the filter type has not been mentioned. Unless there is a particular type of media (eg. carbon) then the media can be rinsed in tank water and put back rather than being discarded.
Regards
Polly