Ah, well in the southern part of the US, a lot of people shorten or link together words. I guess it's a habit so the writer of Forrest Gump is emphasizing that. Where I live, I hear this almost everyday. For example, instead of saying "you all" or "you guys", we say "ya'll." Also, we'll sometimes shorten "doing" to "doin'" I''ll use this in a sentence.--->How are ya'll doin' tonight? You asked the meaning of "tho"...it's the same meaning of "though." The book just shortened the word to show how the character pronounced it in the book. Same goes for "an" and "ole." When the word "and" is said it sounds like "an" when pronounced, and "old" sounds like "old." I suggest you watch the Forrest Gump movie to hear how he talks. You'll notice that his "and" is "an" and "old" as "ole."

Intensee has it covered. Think of it as America's southern dialect & slang - Forest Gump does it very well. Other common ones are: howdy = how do u do? reckon = I suppose, I think ex. cowboy: howdy partner? cowboy: I reckon you heard the news ain't = is not y'all = you all, all of you ex. mother: "y'all ain't even dressed for school yet!" this is all verbal/informal language of course

Abbreviations are shortened representations of words. For example 'etc.' for 'etcetera', or 'e.g.' for 'For example' In Forrest Gump, they are are not so much abbreviations as the writer is trying to convey a particular speech mannerism of the speaker. In this case both 'old' and 'and' have the 'd' removed indicating a less precise manner of speaking. However 'tho' is an USA abbreviation meaning 'though' but it is not commonly used where 'British' english is prevalent. Again, if the author is using it as part of speech, it may also be to indicate slurring, or running together, of the speakers words.

ol' and ole and and an' Those are also dialectical.

It is words of old english which I cannot clearly understand. We acquant such words in classic novels, old translations of Bible and so on. They are not used at present but we have to understand them.