Alright, so we want to add an image into a post or a page. First we log in to WordPress with our username and password. We are taken to the "Dashboard", an overview of the site. From here we click "Edit" under the Posts menu on the left-hand side.
After clicking "Edit", we are shown a list of all the posts available. Chose the post you want to insert an image into and click its title.
Now that we are at the edit screen for the post in question, find where you want to insert the image and put the cursor there and click once. Now that the cursor is positioned, click the "Upload Image" button, as seen circled in the picture above.
A screen pops up. In this upload screen, click the "Upload" button, as circled above.
Browse to the location on your computer where the image is located. Select that image and then press the "Open" button.
Wait for WordPress to import the image. Once it is loaded, fill out the title and caption fields. Description is optional. For link URL, leave this at the default or chose a different place if you want it to link to something else. Chose how you want the image to align (probably center). For the size, anything over 500px wide is probably too wide. Therefore, choose any of the sizes as long as it is 500 or less. Here I chose Medium, which is 500px wide by 375px tall. Now click "Insert into Post".
The image is now in the post where we wanted it. If it is not where you wanted it, switch to HTML edit mode, find the image code, and move it to where it should go. Once everything is set, click "Update Post" on the right-hand side, as shown above. You're done!