The 3-5-3 is probably the #2 youth soccer formations used by coaches when there are 3 or more very strong defenders in the squad and an abundance of midfield players.The formation can be either attacking or defensive, depending on the set up of the midfield.
Role of the 3 Defenders
The back three defenders must have very strong defensive skills and be totally committed to defensive duties. The 3 defenders do not have the freedom to venture forward into attacking positions, except for set pieces where they can be used for ariel dominance
The most common usage of the defenders is to have two of the defenders as marking the opposing two attackers and the third defender acting as a sweeper or covering player.
I would not recommend this formation if the opposition is using more than 2 forwards. ie if the opposition plays a 4-3-3 system, I would normally opt for a 4-4-2 formation.
Role of the Midfielders
The five midfielders are link the defense and the attacker and must work hard from penalty area to penalty area. As with the 4-4-2 system, the wide midfielders act as a defender, making a fourth defender when the opponents are attacking on the opposite side of the field.
The three central midfielders should keep their position in the middle of the field. Often one of the midfielders will remain in a deep position and act as a screen player in front of the back 3 defenders and stop any attacks when possession is lost.
Role of the Forwards
The 2 forwards role is quite simple, to score goals. They should maintain a central position and make sure that they are in “the danger zone”, ready to pounce on any potential shooting opportunity.
The forwards should not be drawn out wide, and should be disciplined to stay within the central corridor. ie no wider than the boundaries of the penalty area
The forwards must be aggressive to the ball and take every opportunity to have a shot on goal.