I need/ Someone else needs

[Deity Psymon]

I haven't quite learned this yet, but I've found myself being unable to complete sentences because I'm not sure how to say this, lol. So how would you probably say I need _________ or someone else needs __________?  

[Acobjum]

Watashi(watashi can be exceptional) (item you want) wo tsukaimasu kudasai. You can also use hoshii if you want to sound cute/childish.  

[Silverfin]

Acobjum

Watashi(watashi can be exceptional) (item you want) wo tsukaimasu kudasai. You can also use hoshii if you want to sound cute/childish.

This translates to "I please use this." Not really what you're going after. Also, "hoshii" is want, not need.

Instead, what you want to say is [item]が必要です(ga hitsuyou desu) / [item]が要ります (ga irimasu). "hitsuyou" is an adjective meaning "necessary", and irimasu (plain form iru) is the verb meaning "to need."  

[Deity Psymon]

Silverfin

Acobjum

Watashi(watashi can be exceptional) (item you want) wo tsukaimasu kudasai. You can also use hoshii if you want to sound cute/childish.

This translates to "I please use this." Not really what you're going after. Also, "hoshii" is want, not need.

Instead, what you want to say is [item]が必要です(ga hitsuyou desu) / [item]が要ります (ga irimasu). "hitsuyou" is an adjective meaning "necessary", and irimasu (plain form iru) is the verb meaning "to need."

If speaking for someone else, though, I assume that が would become を？I believe it changes with ほしい　when you're speaking of what someone else wants, so I just assumed there would be some change with needing something, too.  

[Silverfin]

Deity Psymon

Silverfin

Acobjum

Watashi(watashi can be exceptional) (item you want) wo tsukaimasu kudasai. You can also use hoshii if you want to sound cute/childish.

This translates to "I please use this." Not really what you're going after. Also, "hoshii" is want, not need.

Instead, what you want to say is [item]が必要です(ga hitsuyou desu) / [item]が要ります (ga irimasu). "hitsuyou" is an adjective meaning "necessary", and irimasu (plain form iru) is the verb meaning "to need."

If speaking for someone else, though, I assume that が would become を？I believe it changes with ほしい　when you're speaking of what someone else wants, so I just assumed there would be some change with needing something, too.

No, since hitsuyou is an adjective, you use the subject marker が instead of the object marker を, and いる always takes が. The sentence would be [person]は[thing]が必要です/いります。 The reason for this is that いる translates closer to "is needed" rather than "needs" so the subject is the thing that's needed rather than the person.
The main change with "hoshii" is that you use the verb "hoshigaru" instead of the adjective "hoshii" when you're talking about someone else, along with using を instead of が.