There are features in Croatian that you will see used from time to time. You don't need them in everyday life, but some people use them, and you'll see them in literature (but they are rare even in books).
First, there are several rarely used verb tenses.
The aorist tense is traditionally a past tense, but today it's usually used for events that have happened moments ago, or are about to happen right now. It's usually formed for perfective verbs, but it can be used with impf. verbs as well.
The aorist tense is a single word, usually formed from the infinitive. For verbs ending in -ti, the ending is replaced with the following personal endings:
I'll use abbreviations like aor-1, aor-3pl for various aorist forms, in the same way as for the present tense forms. Here are forms for several verbs (pres-3 and past forms are not shown, as they're not important for forming the aorist if verbs have -ti in inf):
perf. learn →
pozvati perf. call, invite → aor-1 pozvah
uzeti perf. take → aor-1 uzeh
vidjeti see → aor-1 vidjeh
Observe that it's not important if the verb is ‘regular’ or not: only the inf ending matters.
For 2nd and 3rd person in singular, the ending is ‘empty’, so we get nauči and uze.
Verbs with inf ending in -sti and -ći insert a vowel before the aorist endings, -o- in aor-1 and plural, and -e- in aor-23 (the form common to the 2nd and 3rd person):
For such verbs, aorist forms aren't derived from inf. If they have past-m in -ao, it's removed, and aorist forms are derived from it; otherwise, they are derived from pres-3, after discarding the final vowel (which is always -e for such verbs):
pojesti (pojede, pojeo)
perf. eat →
reći (reče, rekao, rekla) perf. say → aor-1 rekoh
Verbs on -ći that have past-m in -kao or -gao shift the final consonant in aor-23 to the consonant used in pres-3:
aor-1 rekoh (past-m rekao)
aor-23 reče (pres-3 reče)
Verbs derived from ići don't fit into this scheme: their aorist forms are always derived from pres-3 (but they're quite irregular anyway):
naći (nađe, našao, našla) perf. find
→ aor-1 nađoh
otići (ode, otišao, otišla) perf. leave → aor-1 odoh
The aorist forms are normally stressed like forms they're derived from: if they are derived from inf, on the same syllable as inf; if from pres-3, like it, etc.
However, in the standard stress scheme, aor-23 is always stressed on the first syllable, regardless of stress of other forms:
The use of aorist is very rare in western parts of Croatia, on more eastern regions, it can be heard in storytelling and expressing immediate action, e.g.:
Ja odoh. I'm leaving now.
Another seldom used part tense is the plusquamperfect tense. It's formed like the common past tense, but there's an extra past form of the verb biti (je +), in the same gender and number as the other past form:
Gledala sam film. I was watching the movie. (fem. speaking)
Bila sam gledala film. (emphasis)
Very similar to the plusquamperfect is the past conditional. It's like conditional, but has an extra past form of the verb biti (je +), again in the same gender and number as the other past form:
Gledala bih film. I would watch the movie. (fem. speaking)
Bila bih gledala film. I would have watched the movie.
This form was used to express intentions and opportunities in the past, but today it's optional, and almost everybody uses just the common conditional.
Then, there's yet another past tense: the imperfect tense. As its name says, it's formed from impf. verbs. It's so rare that I don't recall its endings. I think I've never used it in my life. If you are really want to learn its endings, look into Wikipedia.
There's an interesting feature that was historically much more common: use of indefinite adjectives. So far, I've explained only so-called definite adjectives, which are usually used.
However, most adjectives also had indefinite forms. They could have different stress and case endings. I won't go into details of stress, but the endings in singular are:
As you can see, these look exactly like the noun endings.
Standard Croatian still insists on use of indefinite adjectives. They should be used with indefinite nouns, i.e. when you would use the indefinite article in English:
Vidim crna konja. A see a black horse. (very rare in use)
Then, some adjectives, according to Standard Croatian, have only indefinite forms, regardless of definiteness, and that includes all possessives in -ov or -ev, including njegov his:
Vidim njegova brata. I see his brother. (Standard, but very rare)
Vidim njegovog brata. (this is almost always used)
However, you'll see forms like above in some newspapers, on TV news, and in poetry.