Be aware that all Updates for SharePoint 2013 require March 2013 PU for SharePoint 2013 to be installed first.

To have SP1 installed is as usual our recommendation.

SharePoint Foundation 2013
2881063 The full server package for SharePoint Foundation 2013
http://support.microsoft.com/default.aspx?scid=kb;EN-US;2881063

Download link: http://support.microsoft.com/hotfix/KBHotfix.aspx?kbnum=2881063&kbln=en-us

SharePoint Server 2013
2881061 The full server package for SharePoint Server 2013 and contains also the SharePoint Foundation 2013 fixes so you need only this package.
http://support.microsoft.com/default.aspx?scid=kb;EN-US;2881061

Download link: http://support.microsoft.com/hotfix/KBHotfix.aspx?kbnum=2881061&kbln=en-us

You will see three downloadable packages:

image

You need to download all three and put these into the same folder, before you start the installation.

Office Web Apps Server 2013
2881051 Microsoft Office Web Apps Server 2013 hotfix package    
http://support.microsoft.com/kb/2881051

Download link: http://support.microsoft.com/hotfix/KBHotfix.aspx?kbnum=2881051&kbln=en-us

Project Server 2013
2881062 The full server package for Project Server 2013 and contains also the SharePoint Server and Foundation 2013 fixes so you need only this package.
http://support.microsoft.com/default.aspx?scid=kb;EN-US;2881062

Download link: http://support.microsoft.com/hotfix/KBHotfix.aspx?kbnum=2881062

You will see three downloadable packages:

image

You need to download all three and put these into the same folder, before you start the installation.

Important for all Server Applications listed above:
After applying the preceding updates, run the SharePoint Products and Technologies Configuration Wizard or “psconfig –cmd upgrade –inplace b2b -wait” in command line. This needs to be done on all servers in the farm with SharePoint installed. You can run psconfig in parallel on all SharePoint machines.

You might have you own strategy to run psconfig because it depends on the farm structure and what makes sense to reduce the downtime.

Related Info:

Update Center for Microsoft Office, Office Servers, and Related Products
Common Question: What is the difference between a PU, a CU and a COD?

CHANGE: SharePoint 2013 Rollup Update for the December 2013 Cumulative Update Packaging

How to: install update packages on a SharePoint 2013 farm where search component and high availability search topologies are enabled

SQL Server 2014 and SharePoint Server 2013