Oh don't worry if you don't know how to pray. Just talk to God naturally. He knows your heart as it says in 1 Samuel 16:7. Don't worry about anything. He loves you and has paid for your sins. He wants a relationship with you just as similar as any other relationship you have with friends/family. You don't have to have special words to speak to him. Like you said, just believe. Mark 11:22-24 says "And Jesus answering saith unto them, Have faith in God.For verily I say unto you, That whosoever shall say unto this mountain, Be thou removed, and be thou cast into the sea; and shall not doubt in his heart, but shall believe that those things which he saith shall come to pass; he shall have whatsoever he saith.Therefore I say unto you, What things soever ye desire, when ye pray, believe that ye receive them, and ye shall have them." So just pray and believe.