In finance, leverage (or gearing) is about using debt (other people's money) rather than equity (your own money) for the purchase of an asset. This tutorial explains when this can be good for your business and when it can ruin your business.
There are 2 different accounting methods: Cash Accounting and Accrual Accounting. Check out this article which explains the difference with a story. This makes it really easy to understand the difference between cash basis and accrual method of accounting.