Sentence help

[SkyFox]

Hi all, I'm a bit new here. I've recently started learning again and would appreciate any help.
I'm wondering a few things for the following sentences.

At union station, we saw many different things.
At union station we saw many different things.
To me, he is just a construction worker doing his job
To me he is just a construction worker doing his job
comma or no comma is correct?

I realized this idea can be applied.
I realize this idea can be apply.
I realized this idea can be apply
I realize this idea can be applied
Which sentence is correct? I'm having some big troubles with tenses right now.

[Firefox]

Hi all, I'm a bit new here. I've recently started learning again and would appreciate any help.
I'm wondering a few things for the following sentences.

At union station, we saw many different things.
At union station we saw many different things.
To me, he is just a construction worker doing his job.
To me he is just a construction worker doing his job.
comma or no comma is correct?

I realized this idea can be applied.
I realize this idea can be apply.
I realized this idea can be apply.
I realize this idea can be applied.
Which sentence is correct? I'm having some big troubles with tenses right now.

correct
incorrect

[SkyFox]

Can I ask why for certain sentence?

For example: At union station, we saw many different things
Isn't At union station a defensive clause and thus need a comma?

I realized this idea can be applied
For this sentence, the context was something I learned in class last week. Does that matter it all, or is it still wrong given the context?