Persian language is not as complicated as some other languages. For instance, it does not have gender, as do French and Arabic; dual, as does Arabic, or case inflections, as does German. In addition to the copulative set, there are basically two sets of endings: one for verbs (with the exception of the third singular, which does not take an ending in the past tense), and another for possessive and objective cases both.
Since diglossia (the difference between the formal written and the spoken variations) is one of the main features of the Persian language the spoken (colloquial) variations of the examples and paradigms are often included throughout this site. The emphasis in this grammar is on the written form, because, after learning the rules, the spoken form is largely predictable.
In addition to diglossia, another characteristic of Persian is suppletion—that is, using different roots of morphemes for different tenses, comparison of adjectives, etc. This is an Indo-European feature, which is shared by many IE languages. This should not be seen as alarming. As rapidly as you learned was ~ am (as an English speaker), you will find yourself having no trouble recognizing words in Persian.