how can i install OS X El Capitan says i need to log in as admin its asking for my password, but i don't have one…help!

If you don't have an admin account with a password, then who installed OS X on that computer? Is this a new or used computer? See Writing an effective Apple Support Communities question.

Are you using the guest account to log into your Mac?

This assumes you have not purchased a new Mac, but a used one. That you have not been provided with account access. That you have created very few files. That you were not the original purchaser of this Mac.

If so...

Back up anything that you have created and want to save, use the Mac App Store to download OS X El Capitan and to then build a bootable USB disk, boot that, and wipe your boot disk using Disk Utility, and perform a clean install of OS X.

When this completes, you will boot the new installation, it'll configure itself for you, and you will then have a system that you have the passwords for, that doesn't have extensions or customizations or add-ons that aren't tied to your AppleID, and that's something you can maintain and upgrade.

MrHoffman, the createinstallermedia command requires sudo, which may be tricky if no admin is present 🙂

Sunnyd99, please confirm the status of your user account before you decide on a plan of action…

Open 'System Preferences > User & groups'. Under your username it should state 'Standard' or 'Admin' post back what you find there. Also tell us if any other accounts are listed as an admin.

Also use the 'Apple Menu> About this Mac' to find the current OS X version number. Post that too.

There is a possibility you have an admin account but no admin password, in which case hit return when prompted, no password will make the sudo command fail - you have to add a password in that case.