is it possible to form a triangle with given side lengths
Yes, and no!
Let's say you have been given thrre lengths to use to construct a triangle. Call them l1, l2, l3.
Draw a straight line of length = l1.
Now get a pair of compasses and puting the point at one end of the line l1, draw an arc of radius r = l2.
Now put the point at the other end of the line l1, and draw an arc of radius r = l3.
These two arcs will intersect, but only if l1 < l2 + l3.
If they do intersect, then you have constructed a triangle from 3 given lengths.