From version 78, the player can now access a skills tab from the inventory interface that includes Smithing, Agriculture, and Cooking. Skill is not lost upon death but should not be confused with experience, which is accumulated by killing monsters, and is lost upon death.
Smithing is divided into 4 subskills; General smithing, Tool smithing, Armour smithing, and Weapons smithing. Gaining skill in these will allow you to produce metal items at the anvil with higher durability. Every item produced increases this skill.
Since version 79, smithing also affects the damage done by forged weapons.
Harvesting plants will increase the agriculture skill, and increases the likelihood that a plant will drop 2 seeds when harvested/destroyed. At expert level, you can use the hoe to view the nutrients in the soil, and see nutrient tool-tips over seeds.
High cooking skill makes meals taste better. Every meal produced increases this skill.
Leveling up this skill decreases your false negatives. It also allows you to pan for higher tier ores. Adept level unlocks silver.
Increases the amount of meat gained when animals are killed. At 0 level, only 1% of the meat is dropped.