If I can make one recommendation for anyone starting up with Sketchup:
Learn how to create separate groups of entities (faces,lines,arcs etc.). It is fundamental to working in this application so get to grips with it right from the start otherwise you will struggle with entities getting 'glued' together.
Some associated commands to know are:
1.1(When an entity is selected) Right click>Select>All Connected.
1.2.(With all selected)Right Click>Group
2 Entities inside a group can be edited by double-clicking the object. Press escape when done.
3 Entities inside a group on layer 0 will inherit materials applied to the group.
4.You can also create nested groups (groups containing other groups.)
The hierarchy of groups can be viewed/managed using the outliner tool (Tools menu>Outliner)