You can start from the chapter where the anime ended. Usually, there are online forums or manga communities that can give you the exact chapter number.
The Solo Leveling anime sticks closely to the manga. But there are instances where the anime might condense or expand certain events to create a more engaging viewing experience. The key plot points and character developments remain largely unchanged, though.
The novel leveling style and the mortal style were two common fantasy novels. There were some differences between them.
Leveling up meant that the protagonist would constantly grow and improve his abilities through combat, cultivation, and other methods to continuously improve his level and ability, and finally defeat the strong enemy to become a powerful leader. The main characters in leveling-up novels would usually experience many difficult challenges and tests to continuously improve their combat skills and abilities, and eventually become powerful main characters.
The Mortal Style referred to the main character absorbing natural elements during the process of cultivation to improve his ability and finally reach an extraordinary realm. The protagonists in mortal novels usually had unique abilities such as absorbing natural elements, manipulating wind, water, fire, and other elements. They often interacted with mysterious existences and sometimes experienced the test of humanity.
The main difference between the leveling style and the mortal style was the protagonist's ability and growth process. The protagonist of the upgrade path would usually continue to grow and eventually become a powerful leader. The protagonist of the mortal path had a unique ability and growth path. The growth process was even more magical and mysterious.