I created a slider that slides left to right, but when i load the page, it takes a while for the image show up, does anyone know how to make images load quicker? Maybe make them smaller?

Of course the size of the image is directly related to the time it takes to load. Make sure that your image dimensions already match what you are displaying. In other words, if the original image is 2mb in size 5400x3600, and you have the browser resize to 540x360, that's not a good idea.

In addition, you could have a "spinning/progress bar" displayed until your images are ready.

A spinning bar could be a good solution :)