Bok! moje ime je Carolina. Kako si?  or "Kako ste" for polite version

Je težak govorite hrvatski.

Teško je govoriti hrvatski.

Hvala na ulazu.  

The word "ulaz" (entrance) cannot be used in this context. It makes it impossible to understand. I suppose you wanted to say "Hvala na čitanju" (Thank you for reading) ?

Dovidjenia!

Doviđenja!

Bok - Lesson jedan

I think that as I know so little croatian, I will at least try to speak "Croenglish". I hope it doesn't offend, I'm just following the advices from Benny in http://www.fluentin3months.com/

Hopefully, I will take particular lessons soon.

Bok! moje ime je Carolina. Kako si?

Je teško govorim hrvatski. Hvala na ulazu.

Doviđenja!