Catholic means universal. Roman Catholic means they look to the Pope as the head of the church.
Catholics are our brothers and sisters as much as Baptists, Methodists, etc.
They believe in varying levels of sin; mortal and venial.
Mortal sins can be confessed and forgiven but venial sins don’t need to be confessed.
Mortal sins will jeopardize your soul but venial sins will only send you to purgatory for a time.