Summarize this article:

Use the link or type www.tumblr.com into a web browser.  If you're not logged in automatically, click on Log In, enter your email, click on Next, then enter your password and click on Log In.  If you don't have a Tumblr account, click on Get Started and create an account. It's at the top-right center of the window. Do so until you find something that you'd like to reblog. It's in the lower-right corner of the post you want to reblog. If you like, type it into the dialog box that pops up.  Share the post to other social media by clicking on the Twitter logo in the lower-right corner of the dialog box. Type "@" followed by a username to tag another Tumblr user. Type "#" followed by a keyword to add a hashtag to your comment. Click on the down arrow next to "Reblog" to schedule or queue your post. It's in the lower-right corner of the dialog box. It's in the lower-right corner of the dialog box. The post you want to reblog will now appear on your own blog.

Summary:
Go to tumblr.com. Click on the "Home" icon. Scroll through your feed. Click on 🔁. Add a comment. Click on Reblog.