Can someone help with my dialogue?

I'm decent with dialogue, what do you need?

What's the setting, main plot, and age range?

Those all impact the dialogue, since you won't have people speaking like aristocrats in realistic fiction* or slinging around phrases like "bro, you're salty" in a high fantasy one. Age range is also important because you can't have characters saying "fuck" every other sentence in middle grade (or even YA, and remember: swearing does not an adult book make), and a character in an older YA or adult book saying "you darn brat! I'm gonna kick your butt!"* doesn't work either.

*of course, unless that's a specific choice. One of my realistic fiction characters tends to talk more stiltedly and with less contractions than others since he's generally pretty uptight and intellectual, so him saying something like "I do not understand where you're coming from with that" works better than having the more chill actor say that. Likewise, a character can make the specific choice not to swear, which can either show a trait like innocence, naivety, or a strong religious value and if they do swear at some point in the story, it makes it more impactful. For example, the soft and sweet medic swearing during an intense scene adds more emotion than the street-smart con man doing the same.

Okay so first off, don't censor your swearing like "HOLY $@#%", it looks juvenile and breaks immersion. Either break off the swear like "Holy shi-", "Holy-", or "Holy sh-" with the character being interrupted, or say something like "andrew (Our Supreme Lord and Overseer) swore under his breath; this was not going the way he'd hoped" or "andrew (Our Supreme Lord and Overseer) darted up as the hammer hit his thumb, letting loose a string of curses he didn't know he was capable of." And if you don't want to swear at all, you don't have to. You can also always make up words that fit your setting.

Plot is just the sequence of events, usually following the introduction/rising action/climax/falling action/resolution format.

It's midnight where I'm from, I can help you tomorrow though.

Start the dialogue or start the story?

Pick one.

What are the personalities of your characters, for starters.

…..okay. Give me a sample you have of dialogue.