I used parts of an assembly in the example, but u can use features, curves, drawing, etc in layers.
1° in this example, i will put the nuts and bolts of my assembly in other layer, turn it into work layer, and make all the other parts ''visible only''.
2° them u click in ''layer settings'' icon, and type the layer that will be the ''work layer''
3° right click in the work layer, and ''move selection to layer'', and select all parts ( or features, drawings, etc) and click ok.
now i will set the other layers in ''visible only'', so i can only select the parts that are in the work layer ( the nuts and bolts).