When you rent an apartment, you need to check the lease for rules and responsibilities. For example, some landlords do not want you to have guests spend the night. This is because the landlord doesn't know who your guests are. If they damage the apartment in any way, you will be responsible. Also sometimes a friend who wants to crash on your couch ends up staying for a really long time, and ends up becoming another tenant.
You are responsible for all the utilities you use while living in a rental apartment. This means you will have to pay for the electricity and gas you use. If the landlord pays for any utilities, it will say so in the lease. Once you move in, you will have to call the electric company and the gas company so they can put accounts in your name. Also if you want a phone line, cable or Internet, you will have to call those companies and pay for those services yourself unless the lease says that is included in your rent.
Your landlord is supposed to have access to the apartment you are renting from them. This doesn't mean they can just barge in whenever. It does mean though that with notice, the landlord is allowed to come into the apartment during a reasonable time, meaning not in the middle of the night when you are sleeping. During this time the landlord will inspect the apartment to make sure you are following the rules, and the landlord can also make any necessary repairs. All of this should be written out on the lease. If it is not, do not be afraid to ask the landlord to add that information. It protects both the landlord and you.