Go to http://scratch.mit.edu/ and click on Create in the upper left corner. The Editor page, shown below, will open. This version is Scratch 3. Earlier versions of Scratch had a Pen tab listed with the other colored categories of blocks. Scratch 3 has moved the Pen commands.
To find them, note the small blue block in the lower left of the Scratch home screen. The blue icon indicates additional blocks. Click on the blue icon and a page of additonal commands are revealed.
Click on the Pen icon in the lower left corner of the above menu to reveal a page of options. Choose the option Pen.
Click on Pen as pictured above to reveal the list of Pen Commands as we knew them in Scratch 1 and Scratch 2.
If you use Pen commands in a project, every time you open the project the Pen icon will appear under the My Blocks menu icon.