You should distinguish the `\` at the end of a line which means "ignore the end of line" (then your `cd` command has 2 arguments, too much), and the `\` inside a line which prevents the next character to have a special meaning. 

Then `\;` in your example mean give `find` a `;` argument. Without `\`, the `;` will be seen as a separation between the `find` command and a next one. 

The `\;` is needed when you use `find` with an `-exec` option. An alternative is `+`. You should read the `find(1)` manual for more precisions.