If there is a difference between the masculine and feminine form of the adjective, mente is added to the latter.
Paco es débil. - Paco is weak. Paco canta débilmente. - Paco sings weakly.
David es rápido. - David is quick. David corre rápidamente. - David runs quickly.
El niño recibió el regalo alegremente. - The child received the gift gladly. El niño come felizmente. - The child eats happily. Nosotros hacemos compras fácilmente.- We shop easily. Nosotros ayudamos diligentemente. - We help diligently. Nosotros compramos leche de cabra últimamente. - We buy goat's milk lately. Necesariamente, ella comió verduras . - Necessarily, she ate vegetables.
Tú cantaste dulcemente. - You sang sweetly. Cantas fuertmente. - You sing strongly. Tú descansaste tranquilamente. - You rested peacefully. Ellos hablaron sinceramente. - They spoke sincerely. Ellas conversaron cortésmente. - They conversed courteously