Q: El Capitan Kernel Panic

Boot into Safe mode

<http://support.apple.com/kb/ht1564>

There is a good chance you have a 3rd party kernel extension that is not El Capitan compatible.  Safe mode will not load any 3rd party additions.  You do NOT want to run all the time in Safe mode, but it is a way to move forward until you can either remove or upgrade the 3rd party addition causing problems.

Post the output from EtreCheck

<https://discussions.apple.com/docs/DOC-6174>

which will list all the 3rd party additions along with other information about your Mac setup, which someone in the forum will help you analyze and maybe suggest which 3rd party addition is at fault.

Also if you can find the system panic report, please post that which will also help identify the cause of the panic

<http://support.apple.com/kb/ht2546>

<https://support.apple.com/en-us/HT201753>

Can you boot into the Recovery Partition

<OS X: About OS X Recovery - Apple Support>

The from the menu launch Disk Utility and see if you can repair the boot disk file system.

Hopefully you have a backup for your data which you took before attempting to install El Capitan.  You may need to restore your data.

If you do not have a backup, you can use the Recovery Partition -> Disk Utility -> Restore to copy what you can from the boot disk to an external disk.

That panic happened while attempting to boot from the temporary installation system. There's a slight chance that you might be able to recover by following the instructions linked below, but more likely, you're dealing with a drive failure or some other hardware fault.

Resetting the System Management Controller (SMC) on your Mac - Apple Support

OS X El Capitan: Reset your computer’s PRAM

The startup drive is failing, or there is some other internal hardware fault.

Back up all data on the drive immediately if you don't already have a current backup. There are ways to back up a computer that isn't fully functional—ask if you need guidance.

Make a "Genius" appointment at an Apple Store, or go to another authorized service provider.

If privacy is a concern, erase the data partition(s) with the option to write zeros* (do this only if you have at least two complete, independent backups, and you know how to restore to an empty drive from any of them.) Don’t erase the recovery partition, if present.

Keeping your confidential data secure during hardware repair

Apple also recommends that you deauthorize a device in the iTunes Store before having it serviced.

*An SSD doesn't need to be zeroed.