For images, you have to upload them somewhere else and use an <img> tag to post them. W3Schools has a good reference page on all the attributes for images.
As for text formatting, you'll want to define some styles in your post. You can do that with style tags:
<style>
.some-class-name{
/* formatting stuff here */
}
</style>
once you've defined some classes, you can add them to your <p> tags:
<p class="some-class-name">
Put a paragraph here
</p>
W3Schools has a full reference for all of the different CSS attributes as well as some tutorials. If you want to get really advanced with it, you can upload a style sheet to somewhere like a neocities site and use an @link on all of your blog posts so if you can update the style of all your posts at the same time:
@import url('link-goes-here');
It seems complicated at first, but if you play around with it for a while it'll start making a lot of sense.