As @E pointed out, this is handled in Permalink Settings.
To access these settings, look in the Admin menu on the left side of your screen.
Under ‘Settings’ click on ‘Permalinks’
In ‘Permalinks’ you can see all of your various options for how to format the permalinks.
It sounds like you want to use the ‘Post name’ option. Choose that and ‘Save Changes’
That ought to set you right.