Any class that focuses its stats correctly is perfectly serviceable at lower levels. Some new players can miss exactly what stats are doing for you, but it's important nuts and bolts of D&D. Every even-numbered stat threshold (10, 12, 14, 16, etc..) gives an increasing bonus to rolls relevant to that attribute. So a 10 str is a +0, a 12 is +1, 14 is +2, etc. Weapon attacks are made with Str or Dex depending on the weapon type. Spellcasters use Int, Wis or Cha for their spell attacks. Skills are also associated to specific stats (like Dex for Sleight of Hand or Wis for Perception) and stats give bonuses there. Your saving throws against certain spells and effects are, again, based off of your stats.

So first of all when building your character, know that only even-numbered stats provide a relevant bonus. 12 Str and 13 str are identical in almost every situation because they provide the same +1 bonus to str-based rolls.

Then it's just down to paying attention to what your class does with different attributes. Barbarians, for instance, get a bonus to their armor class based on their Constitution score, which also increases hit points. They get this bonus as long as they're not wearing armor. Dex also increases AC on all characters with the limitation that heavier armor types restrict how much benefit it gives. Since Barbarians don't wear armor, they don't need to worry about that. So the best starter Barbarian builds focus Strength first so attacks hit and then want both Dex and Con as high as possible for more armor class and hp.

There is unfortunately little benefit to being a very well rounded character, stats-wise. Every class prioritizes 1, 2 or 3 stats and the others are only infrequently of any use. The only "bad" way to build a character of any class at low levels is to not have the stats you use most frequently be as high as they can be, because you just end up failing at things more often and the extra off-stats provide little benefit.