Using Cache to make website faster

I am building a website with node.js express webserver and i use Mongo db database.

On my website people can register a profile they can upload pictures and write text.

Now i hear often that many things can be load from a cache then the website run faster.

Now i ask myself if i need to code something into my script to make for example the Mongo db use cache for requests or if i need to code anything to make the browser or webserver to use pictures from cache.

Can somebody help me to understand this cache thing?