This is a very good question, and one which is asked about every two weeks or so in the forum. So we do have two FAQs on it which should help. 
That said, just a reminder that this forum is for people who are using the Samsung SmartThings â„¢ Home Automation platform, so all the questions and answers are assumed to be in that context. Therefore the FAQs are going to make suggestions for things which work with that platform.
So in that context, the short answer is that you use a smart switch, typically a battery operated device, on the wall instead of the regular switch. You can either get one which is designed to cover the original switch leaving it always on power, or you can put a baby lock on the original switch and put the battery operated switch next to it.
There are a couple of other possibilities, but those two choices are the most popular.
As far as which switch to use, as long as you are using a smartthings hub you will have many choices for the switch.
Or if you use a voice assistant like echo or Google home, you will probably find that you very quickly get used to you giving the voice command instead of touching the wall switch. Here again a baby lock, or even just a piece of tape over the switch, can help.