attacking principles provide both coaches and their players with a framework of how you will play in possession, allowing you to build tactics/strategies around these to help you with the desired outcome.
Or
It is the structure of how a team should behave when in possession of the ball and dictates how players should move to create space, manipulate the defense, and ultimately score goals.

There are five attacking principles.
Dispersal
Penetration
Movement
Support
Innovation/Creativity.

Dispersal : this to how your team will create space by providing both width and depth for the player with the ball. This is done when your goalkeeper gains possession of the ball as soon as you’ve done that you want your full backs to create width and depth by moving high and wide up the pitch, Remember your midfield need to come down and triangulate formation in field are very important to maintain possession.

Penetration: This is coming to attack through midfield. This is done to make your team focus on playing the ball through, around or over your opposition by using the midfield, passing ball to no 4 and for no 4, passing to no10 for no 10 passing between two opponents defenders to break lines or playing into the space behind.
Or
Ability for a team to be able to break line collectively or individually. So an example of a way which a team may penetrate may be the setback playing into a center midfielder to play forward.

Movement : this is how players moves off the ball to create space for their teammates or for themselves.
Or
Relate to movement for players between spaces to receive the ball also around as well. So for example, if your opposition team is in a low block defensive principle it may be that the movement of the central forward comes down to get the ball.

Can you remember Fernando Torres Chelsea against Barcelona after Torres lost the ball once he noticed one of his team has got back the ball, he keeps on movement until he got it to score goal?
Here is the highlight.

Support: this has to go with movement in how individual player’s depth support their teammates on the ball either behind, ahead, and beside all this coaches need to teach players how they want it.

Innovation /creativity: This is the innovation of an individual player in attacking third of the field, dribbling one or two players to score a goal or as well as combining with another player to play to -me to -you combination move to score goal.

Watch how Messi did a solo move to score a fantastic goal.

Summary :the principle of attacking is based on coaches perfective either he would like to start his building plan to score goals from defense, midfield or attacking third of the opponent.

All this go with your choose style or system.