Welcome Shane, what is it you need to know?
Using an on screen keyboard should be quite straight forward, I use one all the time albeit with a stylus.
The trick with SketchUp is that it is always listening, so you don't need to do anything special to make it hear what you type.
For Example, select the pencil tool, click and release once to start a line, move the pointer in the direction you want to go, click and release again, then without doing anything else type in the size you want on the keyboard and hit enter. The line will then snap to that size.
Basically all tools work this way, start an action, then type what you want and hit enter to complete. If its not right type something else and hit enter, you can continue to change this until you move the focus by clicking another tool.
The other benefit of an onscreen keyboard is the Modifier keys stick, so you can use them in combination with the tools as needed. ie: Move tool with ctrl makes a copy.
Feel free to ask more questions, but start a new thread outside of this welcome one, they tend to get lost in here.