There is a keyboard out there made specifically for typing secwepmctsin. I figured some of you folks would like to have access to such a thing. Here's the link (http://www.firstvoices.com/en/Secwepemc/welcome). The keyboard link is at the bottom of the page, it's an 'exe' link so when you click on it, it'll give you the download dialog. Here, I hope you know what you're doing. Which means, I hope you have a virus scanner and don't just download and install everything on the internet. With that said, it's a good file.
Skipping ahead to when you have it installed and start it up for the first time, here's a picture of what you're looking for, it'll be hiding in your taskbar. (Win7, and 8 anyway, I'm not sure about windows 10) That whole little place down there with all the tiny icons, the time, and that little arrow is called a couple things, but it's the tray (system tray) and some people call it the notification area. But it's the tray. Click that little arrow and it'll popup a little window with some icons in it.
That little orange one with the "k" on it is the keyman keyboard, click on it. Wait, you're going to be doing this pretty often, I'll tell you how to keep that little icon in the tray all the time. Click the little arrow again to bring up the notification window, click "customize". Here's the window where you can control what's in the tray, it's pretty handy. Find the "Tavultesoft Keyman Engine - Keyman for FirstVoices" dropdown menu and change it to "Show icon and notifications" then hit 'OK'. There you go, the icon should be in your tray now. If you want to go in and change it, easy enough, Customize > dropdown > 'Only Show Notifications' > Hit 'OK' and there you go.
Now let's say you want to get in there and start typing with stress and glottal marks. Click the keyman icon and a little window will pop up, click "secwepemctsin" to turn it on. Now you can do stuff like t́h̓íś, every letter you want to create a stress over, you hit the ";" key, for the glottal mark, it's the "'" key. Cool! You say, then find out you can't turn it off, no problem! Click the keyman icon in your tray again and click "Switch Keyman for FirstVoice OFF" link and you're back to the standard keyboard. Easy enough now to turn it off and on, but you'll have to do it a few times to get used to it.
But wait! There's more!
Keyman has a onscreen keyboard you can use. You can toggle the keyboard on and off with these buttons.
With practice, you can type away and add marks as you go along. Remember, in secwepmc, there's only one stress mark per word. There are a bunch of grammar rules like that, if people would like to see them, I guess I can make a post like that in the future.
Hope you found this helpful!