To insert images to a post there is a little icon above where you type, just left of the smiley face. It is for adding images. That or, if it doesn't work for you, then you would have to upload the image(s) to a free image site (like say imgur) and then add links to the image(s) in the post.
As to the ads, you don't have to have any apps installed other than the ones you picked. Many apps have ads. Most people just don't notice that they say they have ads when the install the app. Which, of course, is what they are counting on.
If the ads only recently started, then I would be looking at what apps you installed just prior to the problem and also what apps were updated.
I would go to the play store (or where ever you got the app(s) from) and see what they actually say about ads.
Additionally, some browsers, even though they don't say they 'have ads' will set it up so that whenever you open the browser app you get an ads page within the browser. I have run into that a lot lately. So far I have only found one that didn't do that. It is called Pure Brower. But many browser apps started out that way and then added this other stuff.