How to set up in custom indicators to achieve the following functions

How to set up in custom indicators to achieve the following functions: Allow buying when the real-time price is above a certain buffer value; allow selling when the real-time price is below a certain buffer value.

如何设置自定义指标以实现以下功能：当实时价格高于某个缓冲值时允许买入；当实时价格低于某个缓冲值时允许卖出。