Hi @betterdaysahead! Welcome to steemit.
For photos, you can either use an external hosting site, like imgur and copy the file link that ends with png (or any image file ext like jpeg)
But for new posts, if the image is saved on the same device you are using to make the post, you can just go ahead and click on 'selecting them' and upload a photo.
For tags, if you wished to use the tag mythreeboys, no spaces in between. For this post tags are showing 'my' 'three' and 'boys'.
Still, best to choose for your primary tag a relevant one that is trending (this is for better chances of post visibility), example, tag 'parenting' is more popular should I be posting about my adventure with my son.
Hope this helps and goodluck! Have fun here :)
That helps very much. Thank you.