"말이야(지)" comes from "말(word)" and "이야/이지/이다(be)", meaning that "I'm saying something..." But this is also used when emphasizing something or attracting someone talking with. Because it depends on the SITUATION and INTENTION to use it correctly, knowing the difference between them is hard to do. i. e. for emphasizing something. 책 좀 빌려 줘. 네가 읽던 책 말이야. = Please borrow the book that you have read. // emphasizing "book" which is modified(sentenced) by "that you have read." i. e. for attracting/gain interests from someone talking with. 내가 어제 낚시를 갔다. = I went fishing yesterday. 내가 말이지 어제 낚시를 갔는데 말이지. = almost the same above, but there is a slight difference in the shade of meaning that speaker wants to gain interests/agreements in topic from the interlocutor. "but can you put it at the end of practically any sentence?" Yes, but not recommended, especially when meeting older people because it is not the honorific form of language in Korean.

"This" is a demonstrative pronoun. Demonstrative pronouns are pronouns that point to specific things. "This, that, these, those, none and neither" are Demonstrative Pronouns that substitute nouns when the nouns they replace can be understood from the context. At the same time, to indicate whether they are close or far, in space or time, from the speaker in the moment of speaking. They also indicate whether they are replacing singular or plural words. "This" (singular) and "These" (plural) refer to an object or person NEAR the speaker. "That" (singular) and "Those" (plural) refer to an object or person further AWAY