I'm a remote worker. One of my main connections to my team is through Slack. The problem was that too often I'd forget to open it up first thing in the morning, not remember till lunch time, and then discover entire conversations had happened without my involvement. To remedy that, here is how to have Slack (or any website) open automatically on startup.
Begin by creating a desktop shortcut to Chrome. If you're unsure how to do this, go to your Start menu in Windows and type "Chrome". When Google Chrome pops up as an option, right click and select "Open File Location".
A File Explorer window will pop open, with Google Chrome inside. Right click the Chrome icon and select "Send To" -> "Desktop (create shortcut)".
You'll now have a shortcut to Chrome on your desktop. Go back to your desktop, right click your new shortcut, and select "Properties".
In the "Target" field append the text " --app=http://mycompany.slack.com", including the leading space and replacing with your Slack namespace. Save your changes.
Back on the desktop, rename your shortcut to the name of the website. In my case, I titled mine "Slack".
Open a new File Explorer window and navigate to "C:\Users\your_username\AppData\Roaming\Microsoft\Windows\Start Menu\Programs\Startup". Drag your new Chrome icon from your desktop to this folder.
Restart your computer and you should see a Chrome window automatically open and navigate to the url you specified in the Target field.
A few things to note. First, depending on how fast your laptop acquires the wifi, it might try to load the website but not have internet access yet. Just refresh the page once you do have internet access. Second, the Chrome window that opens will not have a navigation bar at the top. I actually like this for things like Slack that I want open all day without accidentally navigating away to another site but some may find that annoying. If anyone knows a work-around, I'd love to hear it.