탁자 = table
의자 = chair
You can use those words in sentences like 음식을 탁자에 있어요 (the food is at the table) or like 의자에 앉으세요 (please sit on the chair)
ㅈ &ㅊ are different, you can really hear this one in the tension you use to pronounce. ㅈ is represented as a J and ㅊ is represented as a ch. Sometimes the native pronunciation is really similar, but just think of ㅈ as the J in jump, and ㅊ as the ch in chia seeds.

어 and 오 are really different. 어 is pronounced more as EO, while 오 is just a plain O sound. Lastly 에 and애 are literally the same thing, my teacher told em you just have to memorize when to use them because there isn’t a difference. However, usually the borrowed words use the 에 instead.

What type of instances are you talking about? In writing or when practicing diction?

It all boils down to practice really. After years and years of studying korean, I still find instances of getting these characters mixed up.

ㅈ jieut, there are certain rules for pronunciation but basically can be boiled down to J at the beginning of a word/syllable and T at the end. ㅊ chieut, same deal but with a CH and T. ㅓ (uh, as in Sung) ㅐ(ae, as in Dae)ㅔ (eh, as in utterance meaning 'excuse me?') ㅗ This is an oh sound, I assume you would useㅓwhen a word is spelled that way and vice versa. Not an expert by any means but this is how I learned and it seems to hold up.