Here's how you can display your most popular posts in your sidebar:
- Go to the Design tab in your blog (top right corner if you are on your blog's main page).
- Scroll down a bit and click Add a Gadget wherever you want to add the tag cloud (sidebar on the left or right, or at the bottom, etc.)
- A pop up screen with pop up which says Basics. Scroll down until you see Popular Posts (it should be the second one). You'll see a + button in a blue square right next to it -- Click that.
- Once you click it, another screen will pop up (that says Configure Popular Posts). Configure the settings to your liking.
- Don't forget to save!
Looking for a particular tutorial? Let me know!