There are lots or resources on YouTube
This one from Garmin...
The garmin support website is quite good
There are various videos there if that is your thing...
First step is setting up an online Garmin Account, choosing a subscription plan and setting your emergency contacts.
You should then set up your three preset messages with the message and address list for each...can be phone numbers or emails.
For the subscription plan I suggest starting with the cheapest monthly plan and pay as you go for a few practices messages (50c each way) and tracking (10c a point).
You have to pay the annual activation fee and prepay for 1 month but you can suspend the account for the next month after a couple of days if you are not sure you will be using it immediately. You can reactivate online whenever you want but you do need to do that in your online Garmin account so you need internet service. You can upgrade to more prepaid stuff or to an annual plan at any time if you feel they offer you a better value. You can only downgrade for the next month. It is harder to downgrade from an annual plan so I wouldn't do one of those until you are sure you want it continuously active for 8 mos or so.
Then install the free Garmin Earthmate Phone App on your smart phone and get the bluetooth connection working. This will allow you to sync your account with your Mini from your phone when you have phone data service. You can also operate the Mini and use its GPS to navigate with this app if you download the maps.
You should then install InReach Sync and/or Garmin Express on your PC/MAC to update the Mini firmware via USB. InReach Sync will sync your account info as an alternative to the Earthmate App. Both InReach Sync and Garmin Express will update the Mini firmware.
Note: You should be able to get Earthmate on your phone through the official Apple iOS or Google Android App store. You don't have to get it from the Garmin site.
The Garmin Connect App does not currently work with the InReach Mini, SE or SE+