showing facts or truths

Use of the simple present tense shows that
an action or situation is generally believed
to be true or is a generally accepted fact.

Examples:

Most of the U.S. is in North America.

Spanish and Portuguese are
Romance languages.

The chemical symbol for iron is Fe.

A nickel equals five cents.

The bodies of insects have three parts.

Bronze contains both copper and tin.

showing habits

Use of the simple present tense can also
show that an action or situation is a habit--
it's typical, usual, and predictable.

Examples:

Jim is very punctual.

Mayumi's letters are interesting to read.

He smokes.

They eat in the company cafeteria.

Adverbs of frequency are very common
in sentences with the "habit" use of simple
present tense:

Annie is never on time.

Bob's parents are generally at home
by 5:30 PM.

Dr. Jones is in her office from 9:00 AM
until 4:00 PM five days a week.

Ahmed seldom gets up before 9:00 AM.

Ji-Hyun frequently visits her cousins
in Pusan.

They take a break every three hours.