Do you have to tell someone you're saved before you can actually be saved?
No. Scripture says confession is made with the mouth unto salvation, but that does not mean a person must tell someone else before being saved. Salvation is promised to whosoever shall call upon the name of the LORD; the inward recognition of Christ's work and calling on Him comes first, then confession follows.
Les explains that confession is made with the mouth unto salvation, yet it is not that a person has to tell somebody before he can be saved. He compares it to something good you have experienced: in high school, a favorite bragging right was a car, and salvation should be similar—we should be ready to talk about it at the drop of a hat, as easily as the weather, about what God has done. He knows he is going to heaven not because he deserves it, but because Christ did everything on his behalf. The culmination of becoming a believer is recognizing Christ died for our sin, that we are hopeless in ourselves, and then calling upon Him. Verse 13 promises whosoever shall call upon the name of the LORD shall be saved. Les also uses a swimming pool illustration: on a hot summer day, amid all the kids yelling, the lifeguard hears the kid in trouble, and he thinks God is the same way.
For with the heart man believeth unto righteousness; and with the mouth confession is made unto salvation.