verbs and tenses
when do i use the.....infinitive? the present participle? the past participle? the imperfect? the preterite? the conditional'......and the subjunctive? and the imperative? and what are perfect tenses'
Answering your question with all the details is enough to fill over 2000 pages, so I'll give you some general guidelines:
Perfect tenses are constructed with the verb "haber" (to have) used as an auxiliary:
comer - to eat
he comido - I have eaten
has comido - you have eaten
ha comido - he/she have eaten
Infinitives are used with certain verbs and phrases, like "tener que" (to have to), "deber" (should), and in other cases which I can't mention without typing for half an hour.
Tengo que ir = I have to go
Debo ir = I should go
Also, infinitives often replace English gerunds:
Eating is good = Comer es bueno
I like eating = Me gusta comer
The other tenses... well... there are countless threads dedicated to a specific use of just one tense. Surely you don't expect us to explain here how to use all tenses, right?
Check the grammar reference of this forum for details, and come back with more specific questions.
Your initial question is harder to answer than "Can you explain to me all the theorems and laws used in Maths and Physics'".