Significance of Three Customs Involving String

I've noticed three different customs involving string at Theravada temple service. If by chance anyone is familiar with the significance of any of these; it would be nice to know. The service is not in my native language so I miss a lot of nuances and end up forgetting to ask when I have a chance. 1. The monks sit up on a raised area and occasionally seem to be winding string around various objects creating a web like display. What does this signify? 2. At times long pieces of string are sent through the group of lay followers and everyone tries to hold a piece of the string. What does this mean? 3. At the end of the service people sometimes line up to receive a small string bracelet and a blessing from a monk. Is this just a nice gesture or does it have a particular meaning? Does anyone know what the blessing is for? Thanks for any insights. :)