PRESENT SIMPLE

Human existence has been of description by philosophers and literary people. No wonder. For things that are always true now, we use the Present Simple. Granny has been reading the Cambridge Dictionary.

The matter comes from the online version of the
 CAMBRIDGE DICTIONARY.

CAMBRIDGE DICTIONARY, THE PRESENT SIMPLE; 
CLICK TO ENLARGE

The dictionary says,
"We use the present simple to talk about general facts that are always true and permanent about the world:

Ten times ten makes one hundred.
There is always a holiday on the last Monday in August in the UK."

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Things as 10x10 makes 100 can hold for the Present, as well as the Past, and the Future. This is why we have them for generally true.

For the other thing, granny would not bet a fiver there always will be a holiday on the last Monday in August, in the UK. It is the summer bank holiday. In Scotland, people make it the first Monday of August, and that definitely much more common sense: celebrating the end of the season looks, honestly, a bit prohibitive on pleasure.

Please mind, "betting a fiver" is just a saying, between Jemma and Bob, on how probable things are. The kids do not literally bet, and granny never goes into gambling, either.
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We can compare the Oxford dictionary.
"The present tense (e.g. I am, she works, we swim, they believe) is also called the present simple or simple present. It's mainly used in the following ways:

to describe things that are currently happening or that are currently or always the case (I love chocolate ice cream; my parents are in New York this week; he has fair hair and blue eyes; some birds eat worms and insects)."
OXFORD DICTIONARIES, VERB TENSES

Granny says the definition above is a case of mixed variables. We could refer to the Present Continuous in the same words: we can use it to describe things that are currently happening.

The variables are better not mixed. You can see for yourself with the Modal net, here
TRAVEL IN GRAMMAR CHAPTER 9.2. THE MODAL TIME FRAME

The Present Simple is quite easy, in comparison with the Modal net, and we should work on the Simple first. Granny advises that you read this chapter.
TRAVEL IN GRAMMAR CHAPTER 3. TIME IS LIKE A RIVER

To see if the guidance works for you, try a test.
At best, just think the answers.

Here is granny result.