Setting Work Item Security Scheme on the Work item

Go to JIRA Administration > Work items > Work item Security Scheme

Create an Work item Security Scheme

Once created, click in "Security Levels"

Create as many levels as required

Go back to the Work item Security Schemes page

Click in Edit for the Work item security scheme you just create levels for.

Make sure that the field "Default Security Level" is set to "None".

Go to the project you want to use this Work item security scheme on.

Click in Project Settings

Scroll down to Work item Security

Click in the button "Actions" and then in "select Work item security scheme."

Look for the Work item security scheme you just created and click "Next"

Associate the scheme to the project

Once it's associated, you will have the levels of the Work item security scheme there.

In the levels of the Work item security, click in "Actions" and then in "Edit Work item Security Scheme"

In front of the level you want to edit, click in "Add"

Select the group/project role/user(etc) you want to be able to see the Work items with that level

Make sure you have the Work item Security set on the Work item Screen (Project Settings > Screens)

Go to the Work item you want to set the Work item security level to.

Scroll down to "Work item Security"

Choose the level you want for that Work item and click "Update"

As Work item security schemes are provided by Jira, please take also a look at Configuring Work item-level security for Data Center or Configure Work item security schemes for the Cloud version.