For a list of the SharePoint 2013 updates and versions please see here: http://technet.microsoft.com/en-US/sharepoint/jj891062
Service packs include all previous updates and therefore if a service pack is listed below you do not need to download or Install previous CU, Hotfixes or Security Updates.
Cumulative Updates also include or previous CU, Hotfixes and Security Updates
Please Note: As a result of the new packaging, it is no longer necessary to install the SharePoint Foundation cumulative update and then install the SharePoint Server cumulative update.
Some updates will require to run the SharePoint 2010 Products and Configuration Wizard (Navigate to Start – Microsoft SharePoint 2010 Products – SharePoint 2010 Products and Configuration Wizard)
If the upgrade process fails run psconfig.exe -cmd upgrade -inplace b2b , if you recieve a update not applied error even if the update has been applied run psconfig.exe-cmd installcheck -noinstallcheck
To check the upgrade status you can run stsadm.exe -o localupgradestatus to kick of the process.