Conversation Practice in Pinyin

Josh: ni2 hǎo, wǒ jiào david. nǐ lai2 zì na2 li(3)?  ---> Attention to the "third tone change".
David: wǒ lai2 zì měi guó.
David: wǒ de zhōng-wén bù hǎo. wǒ yào liàn xí wǒ de zhōng-wén.
Josh: nǐ weì shén-me xué zhōng-wén?
David: yin1 wei2 wǒ míng nián xiǎng qu4 zhōng-guó zhu4. --->1. because & so; 2. Since you were talking about things in the next year, it'd be better to say "qu4 zhong1 guo2 zhu4" - to go to China to live, simply indicating the future tense. Nevertheless, your version is gramatically correct. :)
Josh: nǐ míng nián hé shuí zhù/qù? ---> Again, qu4 means "to go".
David: wǒ hé péng-yǒu zhù zài yi4 qǐ. / wo3 he2 peng2 you3 yi4 qi3 qu4. ---> lit: I with friends together to go. [sub+with whom+adv(together)+verb]

Brian: ni2 [ji3 hào / xing1 qi1 ji3] (qu4) gōng zuò?
David: wǒ xīng qī wǔ hé xīng qī liù (qù) gōng zuò.
Brian: ni2 jǐ diǎn (qù) gōng zuò?
David: wǒ cóng zǎo shàng jiu2 diǎn dào xià wǔ yī diǎn ban4 gōng zuò. ---> AM 9:00 to PM 1:30

hěn duō rén jué de zhōng-wén hěn nán.
wǒ jué de zhōng-wén bu2 tai4 nán (le)*. ---> *With "le", it means in the past you thought it was difficult, but not now; otherwise, "I don't think Chinese is difficult".
wǒ zhī dào wǒ de zhōng-wén bù hǎo. wǒ jue2 de wǒ yào liàn xí.

Great job!! Keep it up!!!

Conversation Practice in Pinyin

Josh: nǐ hǎo wǒ jiào david. nǐ lai2 zì nǎ li3?
David: wǒ lai2 zì měi guó.
David: wǒ de zhōng-wén bù hǎo. wǒ yào liàn xí wǒ de zhōng-wén. √
Josh: nǐ weì shén-me xué zhōng-wén? √
David: suǒ yǐ wǒ míng nián xiǎng zhù zài zhōng-guó. √
Josh: nǐ míng nián hé shuí zhù? √
David: wǒ hé péng-you zhù zài (yò qǐ)what is yo4 qi3 ?

Brian: nǐ ji3 hào qu4 gōng zuò? (Do you mean when do you go to work?)
David: wǒ xīng qī wǔ hé xīng qī liù qù gōng zuò. √
Brian: nǐ jǐ diǎn qù gōng zuò? √
David: wǒ cóng jiǔ diǎn zǎo shàng dào yī diǎn bān xià wǔ gōng zuò. √

hěn duō rén jué de zhōng-wén hěn nán. √
wǒ jué de zhōng-wén bù tai4 nán le.
wǒ zhī dào wǒ de zhōng-wén bù hǎo. wǒ juě de wǒ yào liàn xi2.

Overal  very good I can almost understand everything you want to express, 来 is pronounced as lai2，朋 is peng2 友 is you3 but when they combines together 友 becomes (you).

I am quit sure what yo4 qi3 is, if you can put english here I may help you further.

加油  jia1 you2 ↖(^ω^)↗！

Conversation Practice in Pinyin

Josh: nǐ hǎo wǒ jiào david. nǐ lài zì nǎ li?
David: wǒ lài zì měi guó.
David: wǒ de zhōng-wén bù hǎo. wǒ yào liàn xí wǒ de zhōng-wén.
Josh: nǐ weì(wèi) shén-me xué zhōng-wén?
David: suǒ yǐyin1 wei4(Because) wǒ xiǎng míng nián zhù zài zhōng-guó.
Josh: nǐ míng nián hé shuí zhù?
David: wǒ hé péng-yǒu zhù zài yò qǐyi1 qi3(together).

Brian: nǐ nǎ tian1 qu4 gōng zuò?
David: wǒ xīng qī wǔ hé xīng qī liù qù gōng zuò.
Brian: nǐ jǐ diǎn qù gōng zuò?
David: wǒ  cóng zǎo shàng jiǔ diǎn  dào xià wǔ yī diǎn bānban4 gōng zuò.

hěn duō rén jué de zhōng-wén hěn nán.
wǒ jué de zhōng-wén bù taitai4 nán le.
wǒ zhī dào wǒ de zhōng-wén bù hǎo. wǒ juějue2 de wǒ yào liàn xí.

Conversation Practice in Pinyin

Josh: nǐ hǎo, wǒ jiào david. nǐ lài zì nǎ li?
David: wǒ lài zì měi guó.
David: wǒ de zhōng-wén bù hǎo. wǒ yào liàn xí wǒ de zhōng-wén.
Josh: nǐ weì shén-me xué zhōng-wén?
David: yin wei wǒ míng nián xiǎng zhù zài zhōng-guó.
Josh: nǐ míng nián hé shuí zhù?
David: wǒ hé péng-yǒu zhù zài yò qǐ. ( what is yo qi?)

Brian: nǐ nǎ-ge hào qu gōng zuò? (what is hao qu?)
David: wǒ xīng qī wǔ hé xīng qī liù qù gōng zuò.
Brian: nǐ jǐ diǎn qù gōng zuò?
David: wǒ cóng jiǔ diǎn zǎo shàng dào yī diǎn bān xià wǔ gōng zuò.

hěn duō rén jué de zhōng-wén hěn nán.
wǒ jué de zhōng-wén bù tai nán le.
wǒ zhī dào wǒ de zhōng-wén bù hǎo. wǒ juě de wǒ yào liàn xí.

jia  you !!!

Conversation Practice in Pinyin

Josh: nǐ hǎo,wǒ jiào david. nǐ lái zì nǎ lǐ?
David: wǒ lái zì měi guó.
David: wǒ dè zhōng-wén bù hǎo. wǒ yào liàn xí wǒ dè zhōng-wén.
Josh: nǐ weì shén-me xué zhōng-wén?
David: yīn wèi wǒ míng nián xiǎng qù zhōng-guó.
Josh: nǐ míng nián hé shuí yì qǐ zhù?
David: wǒ hé péng-you zhù zài yì qǐ.

Brian: nǐ dōu jǐ hào gōng zuò?
David: wǒ xīng qī wǔ hé xīng qī liù qù gōng zuò.
Brian: nǐ jǐ diǎn qù gōng zuò?
David: wǒ cóng zǎo shàng jiǔ diǎn dào xià wǔ  yì diǎn bàn gōng zuò. 
 
hěn duō rén jué de zhōng-wén hěn nán. 
wǒ jué de zhōng-wén bú taì nán le.
wǒ zhī dào wǒ dè zhōng-wén bù hǎo. wǒ jué de wǒ yào duō liàn xí.