Come whenever you like.

Itsudemo anata ga sukina toki ni kinasai. : Come whenever you like.
itsudemo : any time, whenever
anata : you
sukina : favorite
sukina toki : favorite time
toki : time
ni : at, in
kinasai : come (imperative)
Itsudemo anata ga sukina toki ni kinasai : anytime, you, like/favorite, time, at , come : Come whenever you like.

points;
...demo : any...

for example
nandemo : whatever
nan/nani : what, anything

daredemo : whoever
dare : who, anyone

dokodemo : wherever
doko : where, any place

Itsudemo (sentence(subject)+(predicate)) toki : the sentence modifies "toki" and "toki(time)" modifies "itsudemo"

Itsudemo (anata ga(you))+(sukina(like)) toki : any time , you like, time : any time you like.
If you put "ni (at)" at the end of above sentence,
Itsudemo (anata ga(you))+(sukina(like)) toki ni : means " at any time you like".

You can also use this "...demo" sentence like this;
Itsudemo daijoubu desu. : It's OK at anytime.
daijoubu desu : It's OK.

Daredemo daijoubu desu. : Anyone is OK.

Dokodemo daijoubu desu : Any place is OK.

Because I'm hungry.

Onaka ga suita node nanika tabetai. : I want to eat something because I'm hungry.
onaka : stomach, belly, abdomen
suku : become empty (vacant)
onaka ga suku : become hungry
(suka-nai, suki-masu, suku, suku-toki, suke-ba, suke, sukou, suita)
node : so, because
nanika : something
taberu : eat
(tabe-nai, tabe-masu, taberu, taberu-toki, tabere-ba,tabero, tabeyou, tabeta)
suru : do
(shi-nai, shi-masu, suru, suru-toki, sure-ba, shiro, shiyou, shita)
shi-tai : want to do
tabetai : taberu+shitai : want to eat
Onaka ga suita node nanika tabetai. : stomach, became hungry, so, something, want to eat : I want to eat something because I'm hungry.

You should return the money.

Sono okane o kaesubekida. : You should return the money.
sono : that, the
okane : money
kaesu : return
(kaesa-nai, keshi-masu, kaesu, kaesu-toki, kaese-ba, kaese, kaesou, kaeshita)
verb+beki : should verb
Sono okane o kaesubekida. : that(the),money,return should. : You should return the money.

Kono hon o yomubekida. : You should read this book.
kono : this
hon : book
yomu : read
(yoma-nai, yomi-masu, yomu, yomu-toki, yome-ba, yome, yomou, yonda)
yomubeki : should read
Kono hon o yomubekida. : this, book, read should,: You should read this book.

I'm good at speaking Japanese.

Watashi wa Nihongo ga tokuidesu. : I'm good at speaking Japanese.
Nihongo : Japanese(language)
tokui : be good at
...ga tokui : be good at...
Watashi wa Nihongo ga tokui desu.: I, Japanese, good at : I'm good at Japanese.

futokui : be not good at,be bad at
Watashi wa Nihongo ga futokuidesu. : I'm bad at Japanese.

Watashi wa kuruma no unten ga tokuidesu. : I'm good at driving a car.
kuruma : car
unten : driving
kuruma no unten : driving a car
Watashi wa kuruma no unten ga tokui desu. : I, car, driving, good at. : I'm good at driving a car.

Watashi wa tenisu ga tokuidesu. : I'm good at playing tennis.
tenisu : tennis
Watashi wa tenisu ga tokuidesu : I, tennis, good at : I'm good at playing tennis.

Watashi wa Nihongo ga amari tokui dewa arimasen.: I'm not good at Japanese very much.
amari ...arimasen / nai : not...very much
tokui dewa arimasen : not good at
Watashi wa Nihongo ga amari tokui dewa arimasen. : I'm not good at Japanese very much.