You have to do that during writing your blog.
like write uptil the point after which you want a picture . then insert the picture and write again after that
thank you
Click on the + icon on your blog after you have pressed Enter somewhere in the middle of the blog (i.e. where you want to put in a picture). The first option that you get to the right of + icon is for photo. Click on it and upload the photo you want. Use your computer to do this(not app).