The current ratio checks whether a company can cover the bills due over the next year using the assets it can turn into cash within that same year, such as cash itself, money owed by customers, and unsold inventory. It is a quick read on short-term financial health. You work it out by dividing those short-term assets by those short-term bills, so a ratio of 1.5 means the company has $1.50 ready for every $1 it owes soon.
Above 1.5 is usually healthy. Below 1.0 is a warning sign, since it means the short-term assets do not fully cover the short-term bills. That said, a few excellent businesses run below 1.0 on purpose, because they would rather put their cash to work than let it sit idle.
There is also a stricter version called the quick ratio, which leaves out inventory on the grounds that stock cannot always be sold quickly when cash is needed.