Instil

This means to put a feeling, idea, attitude, behaviour or principle gradually and by continuous effort into someone’s mind, so that it has a strong influence on the way they think or behave. It is related to the mind:

• Parents usually decide to instil good manners into their children from an early age.
• Some would say it is part of a teacher’s job to instil confidence into his or her students.

Install

This has three distinct meanings, deriving from the word stall meaning place or seat. It is related to physical things, equipment and people:

1.    To set in position for use or service:

• The winters were so cold that they decided to install a wood-burning stove.
• I had new software installed on my computer which could recognise my voice and type what I said.2.     To induct someone to an office, rank or position:

• A splendid ceremony was held to install the new governor.
• The college has recently installed its first woman president.

             3.    To settle or establish oneself in a particular place or position:

• They were temporarily installed in a caravan until the renovations were complete.
• She installed herself in front of the fire, keeping the warmth off everyone else.

Footnote: the American spelling of instil is instill.