How does drinking 1 beer at end of day help relax muscles, etc?

Drinking any beer in moderation at the end of a tough day is a safe, pleasant way to unwind. Of course, it doesn't directly relax muscles, but the relaxed psychological effect you achieve will cause you to unclench tight muscles. Most beers you would find at a fuel station are 4-5% alcohol, so drinking one or two will not rot your liver or otherwise cause damage.