The problem i chose to workout was problem number 28 on Sapling. This is a synthesis problem in which you are asked what reactants and in what steps you could form (E) 1,2-dibromo-1-butene from acetylene.
If you follow my arrows i will explain each step. The first thing i notice when looking at the starting material and the final product are the number of Carbons in each. We are starting with an acetylene with 2 carbons and ending with product with 4 carbons. With this known i used the 1.NaNH2 and 2.Alkyl halide reactants in order to add carbons. Since we need two additional carbons i used an ethyl bromide. The next thing that needs to happen is the anti addition of the 2 bromines. This can be done simply by adding 1 equivalence of Br2. This ultimately gets us to our (E)1,2-dibromo-1-butene.