HOW DO WE MAKE MODAL VERBS?

To correctly understand and learn modal verbs or modal verbs, it is important to remember that they never conjugate with the grammatical persons in English (I, we, you, they, she, he, it), in other words:

They never have an infinitive (for example, there is no "to will")

They should never be used in a gerund (for example, there is no "coulding")

They will never have a participle (for example, there is no "musted")

Modal verbs can express anything from needs, probabilities, abilities, requests, suggestions, advice, conditions, to difficult and complex ideas such as "modality"; in this way, its meaning can be transformed depending on the verbs and the related context in the sentence.

Modal of ability:

CAN/CAN'T/COULD/COULDN't

Modal of obligation: 

MUST'T or DON'T/DOESN't HAVE TO

Modal of Probability:

MUST + INFINITIVE or MUST + HAVE + PAST PARTICIPLE