Yeah

"Yeah" is a more casual way of saying "yes". 

Say this to agree with something that a person said:

Yeah, no problem.

Yeah, I actually did it myself.

You can also say "yeah" when you're going to disagree but you want to make your disagreement sound a little softer.

Yeah, but then it'll be blocking one of the outlets.

"Yeah" sounds less formal than "yes." 

(do something) (oneself)

If you do something "yourself", you do it without paying for it or having someone else do it. For example:

Would you like a cookie? I made 'em myself.

This means that the speaker made the cookies at home, rather than buying them at a store. You use the phrase "I did it myself" for things that people usually don't make on their own.

To do something "yourself" is a little different from doing it "by yourself". When you do something "by yourself", it means that there is no one else with you:

I usually eat lunch by myself.

But doing something "yourself" just means that you did it, not another person:

A: Did you make that yourself?

B: No, my wife made it.

(something) actually (is / does something)

"Actually" is a word that you use when you're saying something that you think will be surprising or new information to the listeners. For example:

Wow, this is actually pretty good.

I actually did it myself.

You can use "actually" in several places in a sentence. One place is before a verb, like this:

We've actually had to turn away business.