How do I call the blue line and crossing the line?

Rule 8.4: the ring must be passed, shot with the stick, deflected, batted or legally kicked to another player across each blue line.

• Position of the ring decides. For skaters it is the position of the ring, not the player or the stick, that determines blue line violations.
• A ring on or touching a blue line is in both zones at once and is playable by all eligible players.
• Last player controls it on the far side. If the last player to contact or control the ring when it was entirely on one side of the blue line then controls it entirely on the other side before anyone else touches it, play is stopped immediately (blue line violation, free pass to the other team in that zone with territorial advantage).
• Last player only contacts it on the far side. No one from that team may contact or control the ring within five seconds, or before it completely leaves that zone. Signal a delayed violation and start a five-second count when that player contacts the ring. If the team gains control during the count, play is stopped and a free pass goes to the other team in the zone. If the team contacts the ring again, the count restarts.
• Other team touches it first. Play continues and the violation is dropped.
• After the count. The player who contacted the ring remains ineligible, but teammates may play it again.
• Goaltender throws the ring across the blue line. The same mechanics apply, with the five-second count starting when the ring completely crosses the line.

Source: Rule 8.4 and Annex B, mechanics 17 and 19.