Firstly, position the text cursor where you wish to insert the top of the image. To keep things tidy, it's usually best to put images on their own line or at the very start of a paragraph.
Click on the Insert Media icon in the toolbar and this will open the media pop up.
Click on the Choose files to upload button then locate the image(s) to upload on your computer, or you can drag the files from your computer onto the Drag files here box.
The image will be uploaded and appear under the Details & Dimensions heading, you can then click Insert, or add alt text and set the alignment first (see below).
Alt Text and Image Alignment
Click Edit in the blue bar to view image options.
The Alternative text (alt) is the text that users will see if the image does not load, it is also helpful for search engines and users that rely on assistive technologies. You should enter a description of the image here, for example "photograph of a tree".
By default, images will appear on their own line with text above and below. In most instances this is the best approach as it will adapt well to mobile and tablet views, however sometimes you may want the image to sit within a paragraph. To do this, select either on the left, with text wrapping around or on the right, with text wrapping around from the Alignment / style menu.
Once you have made these changes, click Insert to add the image into the content area.
You can always edit these options after inserting the image by clicking on the image and then clicking on the Insert Media button.
After inserting the image, you can resize it by clicking on it and then dragging the corners to set the size.