The castling is a king move by the rules; this is why in standard chess, for me, the castling must be a king move. And not the king moving onto the rook. For Chess960 things are different. I however also understand that when users are used to something, you cannot just take it awa...
I think it was around the 10th move or so when I tried to castle kingside which I couldn't do. On the 17th move the app let me castle queenside somehow.
What direction can a rook move in chess? As mentioned, the rook is the second most powerful piece (behind the queen). The rook canmove forward, backward or sideways, but cannot move diagonally (like a queen or a bishop). The rook can move up or down vertically on any file. ...
I suggest to watch some videos about the opening you like to play. Look at move orders. Do not move queen before you de esophaguses knights and bishops. Castle soon. Look on line how to mate with different pieces. Look at pwn endings. And go over many games to see how strong players...