GERUNDS AND GERUNDIVES
It’s worth going over the differences between the gerund and the gerundive, given that they can look the same. The gerund is a verbal noun, it’s always active and singular. So if the word you’re trying to translate ticks two or more of those boxes, it’s a gerund.
The gerundive is found in the passive periphrastic construction, where it is used to express obligation. Liber mihi legendus est: “I should read the book.” You can recognise some gerundives in English. An agenda is a list of things which should be done, from ago, to do. A referendum concerns something that must be referred to the people.
The gerundive is a verbal adjective. It is always passive and can be either singular or plural. If the you can’t decide whether the form you’re trying to translate is a gerund or a gerundive, ask whether it describes a noun. If it does, then it’s a gerundive.
The last point on this is that it’s common for Latin writers to use a gerundive phrase to avoid gerunds taking the direct object. So instead of amor legendi libros, Latin likes to say amor librorum legendorum (a mouthful, I know). This is a point of style, rather than of grammar, so just take note of it and, if you want, investigate it further yourself.