I can’t use my hotspot, or login to my Apple ID for iCloud to down load any apps

this Was my mother’s iPhone originally, but she gave it to me when she learned I no longer had mine. Since putting my T-Mobile SIM card in the T-Mobile Iphone, it will not let me log into my Apple ID for iCloud. So I can’t down load anything at all. And it will not show my hotspot, although it says it’s on??? Help please :(