I have 3 switches all at my front door that each connect to a different thing. 1 Ceiling Light, ceiling Fan, and the outside light.
How would I add three smart switches to replace the set up I have now. Who makes something like this. All I ever see is 1 switch.
Can you post a picture? Typically, at least in the US, there are three separate switches in a 3-gang box.
If your switch cover plate is about 9" wide, there are three switches behind it. You would replace them individually.
Welcome!
First, we need to know what country you are in, which model of the Samsung smartthings hub you have, and which version of the SmartThings mobile app you are using. Device options will vary depending on these answers. 
As @Bry mentioned, if you are in the US, it’s simple. Most of the switches which are sold as individual switches can just be placed side-by-side underneath a cover plate for multiples.
If you are in the UK, there are some triple gang switches made that will work with SmartThings, you just have to check the individual models. But they do look a bit different than the dumb switches.
I’m from the US. I’ve put a picture below of the three switches. Is there a certain product that works well with smartthings and then Alexa for these types of switches.
Any switch that is controllable by smartthings can be used with Alexa through the SmartThings/Alexa integration. 
The following is a toggle style, if that is what you’re asking.
@thesmartesthouse can answer any specific questions you have about that model, it’s their house brand.
In addition to what @jdroberts suggested, quite a few people here use GE (Jasco) and Leviton switches. Leviton just has paddle switches, but GE has a toggle switch as well.
