Slang is youth-speak, or specialized speech used by a cultural group.
An example of 1960’s slang is used by Ponyboy in the beginning of the book. Of course, some of these words are still used today, and some are regional and used in different parts of the country.
The words “lone it” mean to go alone somewhere.
I had a long walk home and no company, but I usually lone it anyway, for no reason except that I like to watch movies undisturbed so I can get into them and live them with the actors. (ch 1)
Another example is “digs” as in chapter 1.
And nobody in our gang digs movies and books the way I do. (ch 1)
This means to enjoy something. To “get jumped” means to be attacked and beaten up. A “pop bottle” is a soda bottle.
It’s important to note that “gang” refers to a group of friends more than a criminal organization. In this book, gangs are based on social class, and the lower class gang is called “Greasers” while the rich gang is called “Socs.” They do occasionally get into trouble, but are not the hard-core drug-dealing crime gangs we know today.