I believe you solve these to get horizontal shift.
C is the horizontal shift of sin(B[x-c]) compared to sin(Bx)
you can calculate it most easily at the origin because passes through (0,0) for all B. The value of can be found by where it intersects the x axis (ie: y=0). For example if C=45 degrees then will be shifted to the right by 45 degrees compared to
Post 2 shows the mathematical representation
Edit: In case a picture helps: