A hole in one is very easy to score in a game of Golf. This rare feat would earn you one point. If the hole is a par 4, then you would be three under par, or -3.
You would get a score of one. This would make you 2 under par for that particular hole. Your current score would depend how many strokes it took to complete whole one and two to give your current score at the end of that hole.
Par for the hole.
It is a golf term. It means to score three under par on a hole. If your par is four, you would have to get a hole in one to score a double eagle. If your par is five, you would score 2. This term is an outdated one, and is rarely used because it is rarely applicable.
That would be four strokes. The score would be +1.
A "birdie" is not a specific score, it's one under whatever par for the hole is. If it's a par 3 hole, then a birdie is 2; if it's a par 5 hole, a birdie is 4.
Every hole has a par rating - usually 3, 4 or 5. One under means one less than this. So on a par 4 hole a score of 3 is one under par. This is called a birdie.
Four (4) same as usual one under par
A score for one hole that is one under par is an, "Eagle".
a score of one stroke under par on a hole
It is called a double eagle or a hole in one.