Help me build basically anything?

Not sure about "interesting", but I could teach you a bit of rule of thumb and the like regarding certain kinds of characters.

Offensive units

Characters with good offensive spreads (think, Lucina, Raven, Hana, etc.) are going to want to heavily empaphise on that. I feel some people make the mistake of trying to improve areas like durability when it's generally negligeble as it is, or won't make an actual difference to add more (like surviving more than 2 hits). This usually means Fury or L&D, with emphasis on the latter in conjuction to Desperation + having good assist skills around your team like Reposition, Swap and pretty much always a "Dancer".

Tanks

Tanks aren't limited to physical units, as there are promoninent magic-tanking roles in people like Julia and Felicia, which basically limits their role to Enemy Phase. Raven Tomes are really good here because they add Colourless and basically goes hand-in-hand with Triangle Adept.

Melee tanks tend to prefer QR and take advantage of some form of high attack and probably skill procs (like QR Lukas with his Killer and Ignis).

Characters with innate Distant Counter are really good in particular, meaning Xandre, Camus and BK.

Knowing some of this stuff, you will automatically start aknowledging these and have them fall in it's place. Apparently there's another type of unit in so-called "Duelists", but as far as I know, they only really stand out in simply surviving, rather than outright killing or tanking (and actually killing through it).

I'm not very good at generalising, but you could ask me more-specific questions if you want.

What Nogitsune said is right; you should try to have an idea on how each hero/heroine functions or can play a role in battle. Once you can figure it out, you can have an idea on how to build your team. That's one of the fundamentals to build.

Also another important component is to also look at the stats and IVs (Individual Values) of each hero/heroine. IVs are used in the game in order to balance each character (similar to how it is in Pokemon if you play it). Example: you can have 2 of the same characters, but one can have a high attack stat and low hp stat while the other one can have a high defense stat and a low speed stat for its character (There is an IV calculator on this website to help you calculate each character). Each hero/heroine has their own unique stats as well as pros and flaws. Depending if you have more than one character or not, this can help you decide which to use in battle and which to sacrifice for fodder (for skill inheritance for another character).

Another fundamental part of this game is how do you want to build your team? Balanced? Offensive? Defensive? You pretty much get my point there. This can impact on your battle strategy as well.

I may be able to help you if you also post the stars and IVs for each of those heroes/heroines if you want more specific help. Everyone has their own style in battle depending on whoever replies here, so stick to what will suit you best when choosing. :)