If you have efiled and have a status of "pending", that is because the IRS has not yet accepted or rejected your efiled return for processing.
Except for a few test returns that are pulled for processing early, the IRS won't start processing returns until January 29. So unless yours is one of the early test returns, sometime after January 29 you should hear if your efiled return was accepted or rejected.
See this FAQ: What does pending mean?
It's unclear if the government shutdown will affect the IRS speed this year, but it could if the shutdown is prolonged and if many IRS workers are temporarily furloughed.
Here's another factor to consider which can affect your refund timing:
If you have EIC (earned income credit, aka EITC) or ACTC (additional child tax credit), the IRS will start processing them on Jan. 29, but will not start releasing those refunds until February 15. That means people with those types of credits may not start receiving their refunds until around February 27.
You can monitor the status of the efiled return by logging back into your account, or by using this tool: