Opening Zip file

Purchased a digital version of a woodworking plan. included instructions that had a link to a free version of sketch up. this should have allowed to both open and modify the zip file. can’t do either. help appreciated

You can use SketchUp Free or you could download and install SketchUp 2017 Make which is still available for non-commercial use.

What plan did you get that included a link to download SketchUp?

If I understand correctly, you need to unzip the file to extract the skp file inside. You should then be able to open the skp file with SketchUp Free (in a web browser) or SketchUp Make 2017 (which you will need to download and install).