Try using the introductory videos to help you get up to speed with the program. SketchUp is actually much easier to learn and use than Vectorworks IMO, so you should be able to achieve some skill with the software with little difficulty. The videos can be found HERE - CLICK THIS.
As to your other questions:
You do not type into the Value Control Box (VCB) - what you have referred to as the “measure” box. Just select the tool you want to activate, whether it be the line tool, the rectangle tool, or the tape measure tool and just type your desired dimension after making your selection. If you are activating the rectangle tool, then type the width dimension separated by a comma from the length dimension thus: 25’6,15’. No need to type in the inch symbol or the dash following the feet designation. Of course if you are set up for metric dimensions, just type the numbers separated either by a semi-colon or a comma depending on where in the world you’re located.
Start your work in SketchUp. Layout is a companion to SU and is used to present “paper space” type documents similar to the way drawings are indicated in ACAD or Vworks. You can get a bit more info on how to use LO in these videos - CLICK HERE.
You should have received a new password with the new SketchUp installation. The old password would not work with a different installation.
Also read thru this THREAD - CLICK HERE to see more helpful info about using Layout. (I thank @Barbara (Drischel), an architect and structural engineer from Germany, for authoring the information in the referenced thread.)
Yours is an interesting website, btw.