Your first keep cannot survive the opening wave. Fight, fall, buy a small upgrade and push a little further each time. Three enemies beaten earns one coin. Losing adds a 5% bonus. Fractions are saved, but only whole coins are shown.

The castle fires arrows automatically. Tap an approaching monster to slash it with your pencil — only once every 2 seconds initially. Your taps are weak but helpful.
Every three monsters earn a coin, plus a 5% defeat bonus.
Spend your coins in Upgrade Plans and try again.