On tenses...
A gerund is a "verbal noun." Formed from the verb stem, it's used as a noun. It's somewhat similar to English verb forms ending in -ing (though that form is used as a present participle too). So, there isn't a good map between Latin and English:
Marcus ambulat. (present indicative) Mark is walking. Ambulare est facile. (infinitive) Walking is easy. Uluantem lupum effugi. (present participle) I fled the wolf who was howling. Bene sciuit artem coquendi. (gerund) He new well the art of cooking.
The gerund is formed using the verb's stem plus nd + case endings. However, gerunds are neuter, never plural (despite apparent subject) and never nominative.
Samples
genitive Spes vincendi. He had hopes of winning. ablative ...gratia/causa vicendi. because/for the sake of winning. dative Laudando persuadebat. He was persuade by praising. accusative ...ad vincendum. for the purpose of winning.
A gerundive is a "verbal adjective."
On sequence...
Deponent verbs are passive in form, but active in meaning. Deponent derives from depono, to lay aside. There are only three principal parts to deponent verbs including first person singular (passive), (passive) infinitive, and (passive) participle. In citing form, a deponent verb is often recognizable by virtue of its -or or apparent passive form.
conor, conari, conatus sum (attempt)
imitor, imitari, imitatus sum (imitate)
moror, morari, moratus sum (delay)
loquor, loquari, locutus sum (speak)
sequor, sequi, secutus sum (follow)
polliceor, polliceri, pollicitus sum (fear, reverence)
vereor, vereri, veritus sum (fear, reverence)
obliviscor, oblivisci, oblitus sum (forget)
gradior, gradi, gressus sum (walk, c.f. gradual, motet sung on the cathedral steps)
largior, largiri, largitus sum (suffer, endure, experience)
patior, pati, passus sum (suffer, endure, experience)
experior, experiri, expertis sum (obtain, gain)
potior, potiri, potitus sum (obtain, gain)
Some verbs are deponent only in the perfect like...
gaudio, gaudere, gauisus sum (rejoice)
audeo, audere, ausus sum (dare, c.f. audacious)
soleo, solere, solitus sum (be used/accustomed to)
confido, confidere, confisus sum (trust, have confidence in)
fio, fieri, factus sum (become, be made)
In their characteristic of having an active sense, but appearing passive in form, deponent verbs are similar to the middle voice in Greek. In some derivative languages like French, their equivalents often employ the reflexive, i.e.: Je me suis réjoui. (I rejoiced.)
Of the verbs at the left (sum, habeo, amo, etc.), here is a short list of other verbs that conjugate like them.