3
Click the Edit tab on the ribbon, click Create (see screenshot below), then select the layer you want to add points to in the Create Features pane. Afterwards, just make sure to save your Edits.
2
The short answer is Yes, but creating and editing a TIN surface is beyond the scope of this forum, you need to be training yourself if you are asking such questions. As you have tagged this as an ArcMap question I suggest you head over to esri training and complete the Creating 3D Data using ArcGIS course.
1
You have to save the layer, for instance I add data from a *.csv file and you will work perfect with that data but if you don't save the layer as a shapefile using right click > save object or similar (I have qgis in spanish) you are not going to be able to edit it.
Only top voted, non community-wiki answers of a minimum length are eligible
