Before starting with Lightning Web Component, I would suggest to read this introduction post first.
If you enjoy watching video then you might enjoy below video where I conducted Live coding explaining basics of Lightning Web Component.
In this post, we are going to Show loading image on initial load of LWC. In background we would be calling Apex class to take decision if loading image should be hided or redirect user to some other page.
To make LWC faster, we are going to use @Auraenabled(Cacheable=true) and Platform Cache (Session based)
Below code snippets are self explanatory and would help to get started with calling Apex from Salesforce.