how to find resultant vector from uneven vectors?

When someone draws a force diagram, they might put the arrowhead at the point where the for is applied, or they might put the arrow tail there.  It should be obvious what location is intended.

To figure out the resultant, you may move, without rotating, any (or all) arrow(s).  Place all of your arrows nose to tail.  The resultant is the arrow that would connect the first tail to the last arrowhead.  Move that resultant back to the point of action, if desired.

Use the pythagorean theorem to evaluate the resultant.  For odd-ball angles, you may resolve the vectors into their x and y (and z) components using trig.

It sounds like a 3-4-5 right triangle...