It seems you are trying to pass some value through URL while creating new record. This can be done in following way.
Each field (custom or standard) in Salesforce has its unique ID, and you can use the same to prep-populate the fields on record create page.
To get Custom Field ID
- Go to list of fields, and click on any custom field.
- In URL, you will find the Custom Field ID
To get Standard Field ID
- Standard fields have predefined IDs.
- Check in HTML of Record edit page, and you'll find the one.
Once you get required Field IDs, you can use generic record create URL with parameters. For e.g. Say I need to create a Lead Record, and I want to pre-populate Company and another custom field. ID of custom field is 00N90000003YET3 and ID of Company is lea3, so your URL should look like:
Hope this helps, please write back if you are looking for anything else.