You can see "Insert Images" option just below the box where you put your article description. Click on it. Choose the desired image and enter proper title, keywords and other prescriptions regarding that. Upload it.
Example: Suppose your article is regarding Windows 10 OS and now you chose to insert such an image in the article which covers the start menu and layout of the OS. So your title for the image could be 'Windows 10 start menu' or 'Windows 10 layout and start menu'. Keywords typed should also be similar to the title of the image. Like for the mentioned titles, 'Windows 10', 'Windows 10 start menu', 'Windows 10 layout' are probably good ones.
After uploading the image you will see an embed code below the respective. Copy the code of click embed the code in the article. If you choose for embed, the image code will automatically get copied to the article description box and if you simply copied the whole code then you will have to paste it manually in the article through edit option.
Where ever you want the image to be in the article, just paste the code there. If you want the image to be between the paragraphs, have the code between the two.
The code itself only allows the image to be in center but if you want the image to be in left or right side of the article you need to add 'align=right' or 'align=left' (without commas) just before the ending symbol i.e. '>' of the code.