Image gallery where I can insert images and video
There are a ton of ways ...

You can create your own view, see Flickr-like responsive photo gallery for Drupal 8

Or go for a module like juicebox, or a simple colorbox or (my favorite) photoswipe gallery. These modules use an image field (with multiple values), and then offer a display for the field. For videos you need to make a view using their handlers, not sure which suppports what now ..

You can go further and further .. fe. by using the media_entity (now in core ! media 2.0) with slick_media (more like a slideshow) etc. - see here https://drupal-media.gitbooks.io/drupal8-guide/content/

It really depends on your needs.