I use WordPress Android App to write, update & edit blog posts. It not only saves data (as compared to working on desktop) but is also handy & easy to use.
To add tags in your blog post:
1. Open the blog post in which you wish to add tags. (You can do that before or after uploading the blog post)
2. Click on edit, the right-most icon
3. Just add tags relevant to your blog posts. You can also add excerpt of your blog post.
With Great Love,
Er. Amit Yadav
Life is easy..!