Ascender line is for the top of the letters that go above the x-height: l, h, d, f, k, b.
Capitals line is for the top of all your capital letters and your lowercase t.
X-height line is for the top of all your lowercase letters. The only letters the break that plane are the r and s, they go a little above the x-height line.
Baseline is where all the bottoms of your letters should be.
Descender line is where the bottom of your lowercase q, y, p, f, g, j, z's dip down.