Hello Julia~~
First of all, I must say "thank you" for your passion for learning Korean.
Julia... I guess you are American...? maybe not...? anyway.. you speak English right?
Okay... let's say you are trying to teach English to someone who doesn't know English well. How would you teach him/her? What would be your best advice for him/her?
"KEEP IT SIMPLE!"
Julia, you don't have to understand every lessons with details.
As you said, you are "Beginner".
I really think you are going too far...
Learning language must be step by step; otherwise, rules and grammar points do not make sense.
For example, before learning about 시 or 세.
First, you must know about standard verb, which ends in "-다" (먹다, 쓰다, 보다...)
Second, you must know about 'verb-stem' - 먹 (먹다), -쓰 (쓰다), -보 (보다)...
Third, you must know about the form of "---요", which ends in ---요
(먹다 becomes 먹어요, 써다 becomes 써요, 보다 becomes 보아요...)
Then, you may learn about 'honorific suffix' 시 or 세.
1. about --세, (먹다 becomes 먹으세요, 쓰다 becomes 쓰세요, 보다 becomes 보세요...)
2. about --시, the formation of '시' is 'verb stem' + (으)시 + ㅂ 니다.
(먹다 becomes 먹으십니다, 쓰다 becomes 쓰십니다, 보다 becomes 보십니다...)
Of course, there are a lot more to learn between and after those grammar points.
Julia... my point is this - KEEP IT SIMPLE and learn one by one, one at a time!
I hope you understand my point.
best,
Tim