Infinitive (more exactly named “infinitive construct”) is just the root.
It may be translated to English as a gerund.
Pronoun suffixes may be used with infinitive.
Infinitive can take pronoun suffixes. Pronoun suffixes with an infinitive may express either a subject or an object of the action, dependently on a context.
An infinitive may be used in a conjunction like a noun.
In infinitive of 3-weak verbs the last ה is replaced with ות (in all binyanim, see below). ות or ת is also sometimes added in 3-א verbs (Gesenius).
Infinitive with prepositions
Infinitive X with the preposition כ means (“when it was X”).
Infinitive with the preposition ל means: 1. a purpose; 2. infinitive in English.
היה + ל + infinitive
means “to be going”.
על + noun + ל + infinitive
means that “noun” must do something (expressed by the infinitive).