My future telling palm

My palm with lines on it, 

Helps me see my future. 

I use it to write,

I use it to hold. 

I can show a stop sign with it,

Sometimes it trembles. 

Sometimes it is firm, 

It has nails on which I can put nail polish. 

My palm has the most important thing, 

My thumb. 

Use this to perform an operation, 

Or to plant trees.