nouns, musculine
1) without ending in nominative
PLURAL

N      jeleni         gradovi          momci*
G      jelenA        gradovA         momaka
D      jelenIMA     gradoviMA      momcima*
A      jelenE        gradovE         momke**
V      jeleni         gradovi          momci
L       jelenIMA    gradoviMA       momcima*
I       jelenIMA    gradoviMA       momcima*

*Nominativ, dativ, lokativ and instrumental: changes similar like palatalizacija, only this one is called SIBILARIZACIJA.

K, G, H in front of I is changed to C, Z, S. (K --> C; G --> Z; H --> S)

** here don't go palatalizacija, it's not momče (K infront E).

Sometimes it can be short (-i) and long (-ovi, -evi) plural.

About cases:

This is what I found in grammar:

nouns, musculine

1) without ending in nominative

SINGULAR
N   jelen             grad           momak
G   jelenA           gradA         momka
D   jelenU           gradU         momku
A   jelenA           grad           momka
V   jelenE           gradE          momče*
L   jelenU           gradU          momku
I   jelenOM         gradOM        momkom

Akuzativ (in singular) is the same like genitiv if noun is something alive (person or animal). If noun describe something unlive, akuzativ (in singular) is the same like nominativ.

*momče --> maybe it's not the best example, because here is one change: if you follow the rule that you add -E in vokativ, you would have momKE. That's uncorrect. When you have this (K infront of E), K is changed into Č. So it's momČE. The same happens with G and H infront E in vokativ  (G is changed into Ž; H into Š). These changes are called PALATALIZACIJA.

This is continuing:

If nouns in nominativ end with -č, -ć, -dž, -đ, -j, -lj, - nj, -š, -ž, than in vokativ they have ending
-u
The same is with:
- nouns with -ic and -č(a)c
- nouns with -č(a)k, -ć(a)k, -d(a)k, -dž(a)k
- nouns with -z(a)g * this red "a" means that it's lost in vokativ, for example: nominativ is mačak --> vokativ is mačku
...
- there are more rules, but I don't want to confuse you. This is only for musculine nouns in singular (without ending in nominative).

With endings in nominative, plural and rules for feminime and neuter another day.

Dobro večer!

Sarajevo - Sarajevu (neuter)

Tuzla - Tuzli (female)

Mostar- Mostaru (male)

Also, depends on noun cases:

Idem u Sarajevo; živim u Sarajevu; dolazim iz Sarajeva;

idem u Tuzlu; živim u Tuzli; dolazim iz Tuzle;

idem u Mostar; živim u Mostru; dolazim iz Mostara;

Keep going Anna! ;)

Hvala puno M.K!
Would you please, explain a little more deatiled how I learn about the different noun cases you mentioned?