In terms of cognitive development, you can divide adolescence into three distinct phases.
During early adolescence (around 11-13 years old), young teens first gain the ability to think in abstract terms. They are still mostly focused on the present, but they do start to conceive of the future. They'll begin to extend their areas of interests and get curious about new topics. They also begin to develop a sense of moral reasoning. Some practical changes you'll start to see during this phase are young adolescents beginning to question authority. They will also start to express interest in making more independent decisions about their life, such as who to be friends with, what activities they want to participate in, and how they want to look.
Middle adolescence (around 14-18 years old) means that teens will start looking further into the future. This means they will start setting goals and developing long-term plans. Their moral reasoning will continue and they will start to clarify their own ethical code. As their abstract thinking deepens, their questioning of their world will also deepen. This is a period during which they'll also start experimenting with their personal identity. They will start to understand that they play different roles (e.g. friend, student, athlete, sibling, child, etc.) and have different kinds of relationships with the people in their life. As they try to integrate all these different roles, they will start to construct their own identity.
Finally, late adolescence (around 18-21 years old) will start turning their new curiosity and analytical skills away from internal exploration to external exploration. They will start thinking more about concepts like politics, history and justice. They will begin to formulate opinions on public matters, often quite idealistic, and show little tolerance for opposing views. However, they will also start learning to delay gratification. They are also now thinking about who they will be as adults and what their adult life will look like.