I've heard from a couple of people that they have trouble commenting on Blogger blogs. As I like to get comments, it seemed a good idea to try to help. This will seem like a lot of instructions, but honestly it's easy once you get the hang of it ...
Under each post you'll see little icons for sharing the post on twitter, Facebook etc (feel free to use those if you like!) Just above you should see either 'No comments' or the number of comments already made. Click on that and a box will appear for you to write in.
Under that you'll see 'choose an identity'. If you have a Google or Blogger account, select that and it should fill in your details. Open ID can be used if you have a Wordpress blog. If you don't have one of these accounts, or prefer not to link to them in your reply, or are having difficulty using them, then select either of the bottom two options.
With the name/URL one you can type in your name and I, or my guest, will know who to reply to. You can also add a link to your blog if you wish.
I also allow anonymous comments (this isn't an option with all blogs). If you wish to remain totally anonymous then obviously that's the one to go for. You could add a name or initials to your comment if you would like to make replies easier.
Once you've made a selection, you'll see the bit about proving you're not a robot. On my blogs (and most others) this has been disabled and you can safely ignore it.
Click 'Publish your comment'. Here the comment should appear very quickly. With some blogs you'll need to wait until it has been approved.
Comments can't be altered once you've made them, but you can remove your own and the owner of the blog can remove anyone's.
Hope that helps. Feel free to practise - you can try guessing why I picked the photo to go with this post, or just type 'test'.
Finally you're never obliged to leave comments on blogs, and I know sometimes there's not time, or the internet is being anoyingly slow, or we just don't have anything to add, or get distracted and move onto something else, but all bloggers and guest posters appreciate comments. It makes us feel it was worth writing the post and encourages us to keep blogging.