The question confuses cause and effect.
On a planet without seasons, people would track years in exactly the same way that people on Earth would track months if we didn't have a moon.
That is, we wouldn't.
The Moon has a very blatant regular cycle. Everyone in every society can easily see it and notice the changes from night to night. The Moon, and its months, became very fundamental to society. A person could agree to meet someone at the second full moon from now, and everyone will know exactly when that is. The phases of the moon will even indicate how soon that meeting will be. Even today, traditional calendars such as Hebrew, Muslim, and Chinese are all synchronized with the Moon's phases.
But in today's society, our calendar months don't even match the Moon's phases. Most people that live in cities can't tell you what the current phase of the Moon is now; most of them couldn't tell you even if they were looking at it. Can you?
On a planet without seasons, the year would be indicated by the regular cycle of the position of the stars in the sky. This would be of significance to astronomers and navigators, but for normal people, it would have as much significance as the current position of Jupiter in the sky is to us here on Earth. Effectively no one knows or cares.
If your planet has a large obvious moon, then your people would measure time in months. If not, and there is some other obvious phenomenon with a regular cycle, they would use that.
But I would say that more significantly, if there weren't seasons, your planet likely wouldn't have any civilizations either.
Without seasons, one day is like the next. If you were sheltered last night and you found enough food and water yesterday, you can reasonably expect to do the same today. And you can reasonably expect to continue that way for the rest of your life.
In such a world, why would anyone bother to develop agriculture or technology? Without change and the need to plan during good times for survival during the bad times, people would simply live their lives day to day.
It's the regular predictability of seasons that allows us to know in Spring that we can plant seeds so that if we tend them in the Summer, in the Fall we will be able to gather enough food to last us through the Winter. It's the benefit of co-operating with others to make this process more efficient that brings people together into societies. It's the ability to visualize larger and better ways of doing it that creates technology.
If your people know that today is just like tomorrow, and next week, and next month, and so on, they will have no need to track time, and their society, if it forms at all, will remain stagnant.