Give each finger a job
Let your thumb play the bass string and use index, middle and ring fingers for the G, B and high E strings. Hold an Em chord and slowly pluck low E, G, B, high E. Let each note ring.
Repeat a simple pattern
Count four beats and play one string per beat. Once you can repeat it without looking, try another bass string. Keep your picking hand gently curved and avoid pulling hard on the strings.
Do I need long fingernails?
No. Fingertips work well for beginners; nails are a personal choice for a different tone.