“I always study English on Tuesday.”

FORM:  [base form of the verb] or [base form of the verb + “s” or “es”]

WHEN TO USE IT:  the simple present (also known as the present simple) is used to describe facts, habits, short actions, events, or conditions that are occurring in the present, at the moment of speaking or writing. The simple present is used when the precise beginning or ending of a present action, event, or condition is unknown or is unimportant to the meaning of the sentence.  To explain it differently, the simple present is used to describe something that is happening—but not immediately right now (that would be the “present continuous” verb tense). 

Each of the highlighted verbs in the following sentences is in the simple present tense and each sentence describes an action taking place in the present:

Deborah waits patiently while Bridget books the tickets.

The shelf holds three books and a vase of flowers.

The crowd moves across the field in an attempt to see the rock star get into her helicopter.

The Stephens sisters are both very talented; Virginia writes and Vanessa paints.

Ross annoys Walter by turning pages too quickly.

The simple present is used to express general truths such as scientific fact, as in the following sentences:

Rectangles have four sides.

Canada Day takes place on July 1, the anniversary of the signing of the British North America Act.

The moon circles the earth once every 28 days.

Calcium is important to the formation of strong bones.

Menarche and menopause mark the beginning and the ending of a woman's reproductive history.

The simple present is used to indicate a habitual action, tradition, custom, event, or condition.  Some keywords that accompany these concepts are always, each, every, generally, often, rarely, usually.  For example:

Leonard goes to The Jumping Horse Tavern every Thursday evening.

My grandmother sends me new mittens each spring.

In fairy tales, things happen in threes.

We never finish jigsaw puzzles because the cat always eats some of the pieces.

Jesse polishes the menorah on Wednesdays.

The simple present is also used when writing about works of art, as in the following sentences. 

Lolly Willowes is the protagonist of the novel Townsend published in 1926.

One of Artemisia Gentleschi's best known paintings represents Judith's beheading of Holofernes.

The Lady of Shallot weaves a tapestry while watching the passers-by in her mirror.

Lear rages against the silence of Cordelia and only belatedly realizes that she, not her more vocal sisters, loves him.

The play ends with an epilogue spoken by the fool.

The simple present can also be used to refer to a future event when used in conjunction with an adverb or adverbial phrase, as in the following sentences. 

The doors open in 10 minutes.

The premier arrives on Tuesday.

Classes end next week.

The publisher distributes the galley proofs next Wednesday.

The lunar eclipses begin in exactly 43 minutes. 

SPELLING THE SIMPLE PRESENT IN THE 3RD PERSON SINGULAR (he / she / it):

Look at how the base form of the verb ends to determine how to spell a verb in the 3rd person singular.