For such questions it is convenient to choose the "base" to be a segment that is aligned with one of the coordinate axes. Here, the horizontal segments will serve. Their length is the difference between the x-coordinates of the end points, -2 -(-6) = 4, for example.
The height is measured perpendicular to the base, so will be the difference between the y-coordinates of the horizontal segments: 2 -(-4) = 6.
No, this triangle is not equilateral. This triangle is scalene. All three sides are of different lengths, which is why it's scalene. In order to have an equilateral triangle, all three sides need to be the same length.
