If you look in the page on github (easy to find, but it is here: https://github.com/Neverball/neverball- … ntities.md ), the entity you use in radiant to place the ball in Neverball is "info_player_start".
To add an entity in radiant, right-click when hovering the mouse over the grid window on the left side. This will bring up a list of entities that you can add by clicking their names. I forget where info_player_start is, but it should be easy to find in this list.
Another way of adding an entity is to bring up the entity window. Looking at the top of the radiant window there should be an icon somewhere that will say "N" and something like "entities" when you hover the mouse over it. There is probably also a menu item in one of the dropdown lists. Another way is to press the "N" key (not sure if capslock matters). Before doing this, you might have to have click/hover over the grid or 3D cam window to set focus on them.
When you get to the entity window, you will see in it a big section and a small section. The small section will have a list of entities. You can press a key to scroll to an entity starting with the letter you pressed. But before you do this, you might have to set focus on this section and not only the entity window. When you find the entity you want I think dbl click or select it and press enter. Then you will get the entity in the grid/3D cam windows.
ps darnit as usual I am writing tips 90-100% from memory
pps if you press f1 you can get a help document for radiant in a web browser. This document can be helpful when you have a lvl editing quiestion that is directly pertinent using to radiant but not to Neverball mapping. Also you can find abt out some really useful brush/entity manipulation tools like regions, hiding/unhiding things, texture lock, etc. Keep in mind a lot of this document you can forget if you are only using radiant for Neverball.
darnit you might be able to find the same document onilne but I am forgetting where
It the it's level set: http://neverforum.com/fmpbo/viewtopic.php?id=29226/19/17: a bit of help needed here, plz: http://neverforum.com/fmpbo/viewtopic.php?id=2988
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