Each role in Dota 2 is unique and has a different behavior from one another. Playing more games will let you learn more about these roles. Most players focus on increasing their MMR so they explore all roles. Some choose to have Dota 2 MMR boost to climb up the ladder faster. Learning to play on each of these roles will help you a lot.
Carry
This is the golden boy or girl of the team deserving all the creeps on the map. The team relies on his or her farm. This physical damage dealer is the center of the team. The potential of a carry will be at its best closer to the late game because of the items. Controlling the lane will decrease the number of creeps the opponent can kill. Some of the best carry heroes are Faceless Void, Anti-Mage, and Phantom Assassin.
Mid-Laner
Heroes who prefer the middle lane are those who need some levels to become stronger. The mid-laner should have enough skill to win the lane because his or her power is in the early and middle of the game. These heroes do not stay on the middle lane throughout the game after reaching enough level. He or she starts snowballing into the ranks of the enemies to give the advantage to his or her team. Invoker, Monkey King, and Kunkka are awesome mid-laners.
Hard-Laner
The job of a hard-laner is to gather gold and experience even if it means losing the lane. Uncomfortable laning stage is common to this role. It is vital to see all opportunities to gain no matter how little of an advantage. This role needs decent durability or great escaping tools. A hero who could take on a lot of damage while earning gold and experience is the best choice. Examples are Beastmater, Tusk, and Brewmaster.
Semi-support
This role gets the basic artifacts without stealing gold from the upper roles and aims to earn free gold. He or she wards the map and buys the smokes. Semi-support heroes only need Blink Dagger and Ultimate to be useful in the team. The best choices are Lion, Phoenix, and Grimstroke.
Support
Map control lies in heroes with the support role. Ganking and saving abilities to help the team win the laning phase is necessary. Coordination with the team is also crucial. Spending on wards and supportive artifacts make this role vulnerable. This role usually sacrifices for the carry. Lich, Lion, and Dazzle are wonderful supports.