Let's start with making a path from selection:
- Select some area using any selecting tools and commands.
- In the Effects panel, double-click the "Path from Selection" thumbnail.
- In the dialog box that opens, define "Tolerance" (must be between 0,5 and 10 pixels). For example, to make the path as close to your current election edges as possible, type "0,5". To make it smoother, enter "2,0" or an even higher value.