It's literally liquid solder/flux mixed. You can "paint" it on with a brush. It melts easily under a torch or even lighter and makes a very strong bond.
This is a picture of my fenders one day of soldering skill apart. The first day was horrible, day two was amazing. Serious, only one day apart using electrical solder.

Solder paint made my life even easier. My soldering work past that point got much improved and with less headache and effort.
Don't be intimidated, it will come to you.
