Yes, there are design examples in the manual for both LRFD and ASD methods.
Note that welds and the area of the aluminum alloy within 1 inch of the weld will have greatly reduced allowable stresses.
Weld area and stress are computed as for any other material. The configuration geometry of the railing design will dictate the stresses based on either a 200 lbf point load or a 50 plf distributed load. If the post spacing is less than 48 inches, then the 200 lbf point load will control. If the spacing is greater than 48 inches, the 50 plf load will control.
The bending moment at the bottom of a rail post will determine the minimum weld size in most applications.