Planta vs. suela
The Spanish language contains many words that can confuse non-native speakers because of their subtle differences in meaning. 'Planta' and 'suela' can both be translated as 'sole' in English, but they have different uses in different contexts.
Planta
The word 'planta' has several meanings, but when related to 'sole', it typically refers to the bottom part of the foot. It can also refer to the floor level of a building or a plant.
Me duele la planta del pie después de correr.
(The sole of my foot hurts after running.)
Viven en la primera planta del edificio.
(They live on the first floor of the building.)
La planta creció mucho durante la primavera.
(The plant grew a lot during spring.)
Suela
'Suela' specifically refers to the bottom part of a shoe or sandal - the part that comes in direct contact with the ground.
Necesitas zapatos con una suela más gruesa para escalar.
(You need shoes with a thicker sole for climbing.)
La suela de mis botas está desgastada.
(The sole of my boots is worn out.)
Estos tenis tienen suelas antideslizantes.
(These sneakers have non-slip soles.)
Summary
'Planta' and 'suela' are two Spanish terms associated with the English word 'sole', yet with different contexts. 'Planta' often refers to the bottom of one's foot or other definitions not related to footwear, while 'suela' is specifically used for the lower part of a shoe.