Managing images is carried out through the Media Link on the side panel, or through the media browser when inserting or attaching images.
You will have more control within the Media Manager through the side panel as this contains more features.
Best practices:
Most images coming from cameras will look something like this; IMG_100020.jpg or IMG_6547.HEIC, or similar, so renaming is essential as the name does not give any clue as to what the image actually is.
Image names are as important as the image itself.
Name/Rename your images to a relevant name that will help understand what the image is, this will also help Image searches which can mean your website gets better hits in the search engines.
Use only those recognised file types for browsers;
JPG or JPEG, GIF, PNG, SVG, WEBP and MOV, MP4 for video. Any other image types convert them to an appropriate type prior to uploading.
Naming conventions:
Use a - (dash or minus character) instead of spaces.
Try to use only letters and numbers and try not to use special characters, eg. apostrophes ( ' ), ampersands ( & ), commas ( , ), full stops ( . ), exclamation marks ( ! ), etc.
Although capital letters are OK it is best to use lowercase letters as two files such as Filename.jpg and filename.jpg may conflict.
Size of image:
Consider your customer when creating your images as they may be on a limited Data Plan and count every single megabyte, you can reduce your image to its smallest size to fit well into your website.
If possible run an image optimisation using an app such as imageoptim or similar, this will reduce the byte size of the image without affecting the quality of the image.
Creating thumbnails for images is a good idea as initially the web page can show these smaller faster loading images before showing the larger version, this can be done within the Media Manager but a better result may be obtained using a simple graphic editor such as GIMP or Affinity Photo, or if you prefer Photoshop.
When using the Create Thumbnails button an image will be created to the designated size and store the thumbnail as exactly the same filename within a folder called thumbnails, if this folder does not exist then it will be created prior to the thumbnail creation.
Where to put your files:
So you can find files easier it is best to create folders, for your products store images in the products folder.
When editing categories you can click a button to create all the folders for each subcategory ready for use.
So clicking create folder button for your products; SHOP - MECHANDISE - T-SHIRTS the system would create a shop folder and then inside this it would create merchandise folder, then inside this a t-shirt folder then inside that a thumbnails folder, all ready to store your images and files.
That way everything should be easier to find as you know your t-shirt images are all in that folder.
This also makes it easier to clear out any unused or old images as each image shows how many times it appears in content throughout the website.