Hello @Walkingforde After downloading a mod apk you need to locate the mod in your file manager/explorer then click on it and select the install option. if you get a warning that you cannot install apps from unknown sources then simply go to the settings and search for the 'install apps from unknown sources' and enable it. this doesn't mean that our mods have viruses but it is because that the app hasn't been downloaded from an appstore such as Get Apps from Xiaomi or Google Play Store.
now i assume your question has been answered so i am moving this thread to answered questions. if you have any other doubts or questions then you can contact a staff member or make a new thread.