Regarding security levels

[anjali s]

How many security levels are there in Jira ?

[Bharath Kumar Kappala · Accepted solution]

Just go into the Project Setting for the particular project and make changes to the Permission Scheme

Add all the user to a group or a project role or individual user can be given access to the Edit issues permission, here is the screen shot for you

[Bharath Kumar Kappala]

You can also set the permission to 

• Application access (Any logged in user

which will allow all the users with Jira access to edit the issues.

[Joe Pitt · Accepted solution]

Unless you have a plugin or scripting permissions are controlled by the permission scheme applied to the project. Being an administrator DOES NOT convey any special permissions other than what is in the permission scheme. Many of us seasoned users use project roles to control project access and permissions. It gives the best granularity. Pick a UK user and a US user and compare what permissions they have based on your use of project roles or groups.