in the upper right hand corner of the GrabCAD web page is an icon of your profile picture. If you hover your mouse cursor over this a drop down will appear and the top option should be "create." Click on this and then follow the screens. upload your CAD files and renders (Be sure to include all parts to an assembly) a .zip file is best for these types of files and if you can include STEP or IGES files that is always greatly appreciated. If you have renders or screen shots upload them too. Write a nice description and enjoy feedback and sharing.
click on "Create"
Click on Library Model to upload a public project.
Click Select files.
While your files upload, fill out all the boxes as best you can. If you would like others to be able to upload renders or other file formats, be sure to click the permissions check box. When the files are finished uploading and you have finished with the description, press publish and you are done.