A white mucus is coming out of my Betta fish's mouth what is it and is this normal looks like a trail of white thin mucus?

Your fish has mouth fungus and will probably die. If you do a water change ASAP and then follow the basic rules below your fish may recover but it is unlikely. Your local pet shop may have some "Fungus cure" amongst all the aquarium medications they sell and it may help but the most important thing is to know and follow the basic rules in future. The basic rules of fishkeeping also apply to Bettas. They are :- 1 inch (2.5 cm) of fish needs at least 1 gallon (3.5 ltrs) of water. A Betta is classed as a 3 inch (7.5 cm) fish :- Every tank needs a permanently running cycled filter. Every tank needs at least 50% of its water replaced every week. Bettas need to be kept at around 78F (26C) and fed a good quality food morning and evening as much as it will eat in 15 minutes. Never ever leave uneaten food in the tank to rot. It will poison the water and the fish may well die.