Caching and a CDN both make your website feel faster, but they do it in different ways. Caching cuts down on the work your server (or your visitor's browser) has to repeat on every page load. A CDN cuts down on the distance your website's files have to travel to reach the visitor. Most fast-loading sites use a combination of both, not just one.
What Caching Does
Caching means storing a ready-made version of something so it doesn't need to be rebuilt or re-downloaded from scratch every time. There are two kinds you'll run into most often.
Server-Side Caching
Every time a visitor loads a page, your hosting account normally has to run your website's code, pull data from the database, and assemble the final page. Server-side caching (for example OPcache for PHP, or a caching plugin on a WordPress site) saves a finished copy of that work so the next visitor gets served the ready-made result instead of making the server redo everything from zero. This reduces load on your hosting account and speeds up every visitor, including first-time ones.
Browser Caching
Browser caching works on the visitor's side instead. When someone visits your site, their browser downloads your logo, stylesheet, and other files that rarely change. Browser caching tells that visitor's browser to keep a copy and reuse it on their next visit, instead of downloading the same files again. It only speeds up repeat visits from the same person, not a stranger's first visit.
What a CDN Does
A content delivery network (CDN) takes copies of your website's static files, such as images, CSS, and JavaScript, and stores them on servers spread across different locations around the world. When someone visits your site, they download those files from whichever CDN location is physically closest to them, instead of from your main hosting server. This matters most when your visitors are spread across different countries or continents, since the physical distance data has to travel affects loading speed.
The Key Difference
Caching saves your server (or a visitor's browser) from repeating work it has already done. A CDN shortens the physical distance your files have to travel to reach a specific visitor. One is about avoiding repeated effort; the other is about geography.
Do You Need Both?
Caching helps almost every website, regardless of where your visitors are based, because repeat work is wasted work no matter the audience. A CDN's benefit depends more on your audience's location. If most of your customers are browsing from within Kenya and your hosting account is already based in or near the region, a CDN may add a smaller improvement than caching would. If you expect visitors from further afield, or want the extra layer of protection most CDNs include against bot traffic and basic attacks, setting one up is still worth doing.
The two aren't competing choices. Turning on caching and adding a CDN work on different parts of the problem, so using both together gives a bigger combined improvement than either one alone.
If your website still feels slow after enabling caching, the bottleneck is more likely to be unoptimized images or a heavy theme/plugin setup than a lack of a CDN. Check those first before adding another layer.
For the steps to turn browser caching on for your hosting account, see How to Enable Browser Caching to Speed Up Your Website.