You think you're going to get a better answer by asking that here rather than by reading the Wikipedia article or a media company's summary of what Hamas is?!

As neutrally as possible:

Hamas is an organization in the area of historical Palestine. It has been governing the Gaza Strip, a small piece of land between Israel, Egypt and the Mediterranean Sea, since 2007.

Ever since then, Israel has been blockading the Gaza Strip. Every few years, eg. in 2014 and 2021 and now again, Hamas fires rockets at Israel or otherwise attacks it, to which Israel responds with airstrikes.

Palestinian narrative: Israel is a settler colonial state that has taken away Palestinian land and is imprisoning Gazans in Gaza. Fighting against that is legitimate resistance against oppression. Israel's goal is ethnic cleansing of the Palestinians.

Israeli narrative: Israel is a safe haven for the historically oppressed Jewish people. Arabs have plenty of other countries for themselves. The aim of Hamas is to eliminate the Jewish state and maybe even the Jewish people. Israel is doing its best to avoid civilian casualties in its airstrikes against Gaza.

The actual truth: There is no such thing as the actual truth. There is a reason why this is the most difficult conflict in the world.

inb4 people with strong opinions on both sides tell me their opinion is obviously right and the above is nowhere near neutral

Hamas is a terrorist organization currently engaged in a war with Israel. They are the defacto rulers of the Gaza strip, and most of their members are in Gaza. However, many Hamas leaders live outside of Gaza.

They are listed as a terrorist organization by the US, Canada, UK, the EU, and more.

Their charter declares their goals to be the violent destruction of Israel, the establishment of an Islamic caliphate in the land of Palestine, and killing all Jews worldwide.

https://simple.m.wikipedia.org/wiki/Hamas

Hamas (Arabic: حماس, acronym of Harakat al-Muqawama al-Islamiyya, Arabic: حركة المقاومة الاسلامية, literally "Islamic Resistance Movement") is a Palestinian Sunni Islamist militant group. It was started in 1987 during the First Intifada by Ahmed Yassin and Abdel Aziz al-Rantissi as the Gaza branch of the Muslim Brotherhood organization in Egypt. In the 2006 Palestinian election, Hamas got 74 of 132 seats in parliament and controls the Gaza Strip. The group wants to build a Palestinian state based on Sharia law in the area that is now Israel, the West Bank, and Gaza Strip. Hamas does not recognize the State of Israel.[2] it has been designated a terrorist organization by many countries due to its attacks, including suicide bombings and rocket attacks.

Depending on the narrator, they're either freedom fighters or terrorists. The question should be why and how does Hamas exist? They didn't pop up one moment and started killing people.

If you're really interested, read some different sources or listen to some podcasts from both sides and you'll have a bigger sense of things.

It’s an organization that controls the palestinian people. It’s a government, but there hasn’t been an election in seventeen years.

That’s about all I know