line changes

Question
QUESTION: During line changes/ substitutions, how do the players know when to head for the bench- does the coach signal in some way?

Is the goalie allowed to take a shot or advance the puck by passing, skating...?

ANSWER: Hi Martin,
Well at the younger levels (mite/squirt) they may play "buzzer" hockey. The clock is set for 1-2 minute shifts and when the buzzer goes off, the kids stop and change-up. Higher levels vary. Kids are taught to take short shifts anywhere from 30 seconds to 1 1/2 minutes. Some coaches (i.e. UNH men's coach) whistle loud enough and the skaters can hear it. For some reason, the D seem to change-up more smoothly than forwards (probably because there are less).
The goalie cannot pass the blue line. He can skate and shoot up to that point. Some plays such as breakouts are designed with a pass back to the goalie so the goalie can generate the play. Goalies can also get assists on goals and some have even scored!

---------- FOLLOW-UP ----------

QUESTION: In the NHL, how is the signal to change the line communicated?

How often does a goalie score (I assume, usually, in an empty net)?  When was the last time that has taken place?

Answer
In the NHL they change like any other level. The coach calls the center for the next line to go and the wings look to see who they will replace. Same with the defense. The assistant coach usually calls the next "D" pair.

It's not often a goalie scores. Of course open nets would be easiest. I cannot remember if there has ever been a goal scored with a goalie in net by a goalie. Most notable puck handlers were Ron Hextall (Phil. Flyers) and Billy Smith (NY Islanders). The last goalie to score was a while back and may have been a Pittsburgh Penguins goalie, but I do not remember. Obviously it is a lot easier for a goalie to get an assist and isn't unusual for a goalie to finish the season with a few points!