what country are you in?  In the UK it can be the case that a contract is formed on the exchange of money, but you'd be best trying to get legal advice (Shelter for example)

You've signed the agreement - it's immediately legally binding. So no; you can't pull out.

You can only end the agreement with the written agreement of the landlord; IF they agree, expect financial penalties. 

You signed the lease so why would you think you are not obligated to live up to it?  You are bound for the full term.  If you would rather not move in, go and talk to the landlord.  He may let you out, but not without penalty because he may have to advertise and show it all over again and that's costly, and you will owe rent until he can rent it to someone else.

You signed the agreement, so you are legally commited to obide by the contract, unless the landlord agrees to you terminating that contract

you are contracted and they can sue you for the rent

No. The rental agreement was legally binding the minute you signed it. It does not matter that you have not paid anything yet.  They can charge you what ever lease break fee was stated in the agreement you signed. 

You sign, you have a contract.

Once you sign an agreement to rent,  you are committed to fulfilling its terms unless the landlord agrees to release you from it. If they do agree to release you from your rental agreement, be sure to get it in writing and signed by your landlord.

Some tenants will try to find a replacement renter to move into the unit and sign a new lease with the landlord. That would entail having your landlord screen the other person and having them sign a new lease, which would require the landlord’s consent.

Unsure. Ive never done that. Why sign in the first place?

You CAN pull out. The issue is will they ruin your credit or come after you.

You signed a contract and want to know if you can pull out out of the contract.  No one here can answer your question without evaluating the contract.