For context, I’m Palestinian by descent but I’m trying not to be biased. In my opinion what you have is a fundamental conflict of interest, where two sets of people have a reasonable claim to a piece of land.
Prior to 1948, what is now Israel was the British mandate of Palestine. Both Jews and Arabs lived there. Obviously during the Second World War, Jewish people suffered horrifically, and after the war there was a big movement towards giving the Jewish people their own homeland where they could go if something like they should ever happen again. Totally reasonable.
In 1948, Israel was established. In order to allow this, and for the new Jewish state to have a Jewish majority, lots of Arab people (including my family) were forced from their homes. This is why you have refugee camps full of Palestinians. This is why Palestinians want that land back. Also totally reasonable.
There is a state of Israel, and two Palestinian Territories, the West Bank and Gaza. These are called the “occupied territories”.
Jordan captured the West Bank in 1948, and Israel captured it back in a subsequent war in 1967. This is why it is said to be “occupied”. Similar with Egypt and Gaza.
Palestinians want their own state. Some hardline Palestinians (including Hamas, who rule in Gaza) want to abolish Israel and have the whole area as Palestine. Some hardline Israelis want Israel to include the Palestinian Territories. Most moderates think a 2 state solution of Israel and Palestine existing side by side is the way forward.
There is a highly contentious issue of settlements where Jewish Israelis (I specify as some Israelis are not Jewish, some Palestinians got Israeli citizenship) build homes on Palestinian land, which is seen as provocative by Palestinians. Most recently, some Jewish Israelis have laid claim to Palestinian homes in a neighbourhood called Sheikh Jarrah and Palestinians have been evicted. This has caused a lot of ill feeling to say the least and has sparked the latest conflict.
This is deliberately simplistic as requested. It’s a very complex conflict and sadly one which I don’t see ending any time soon.