The two main ones that I know are shounen and seinen (if that is how you spell them). I’ve also heard of other names like Isekai and ecchi. I’m not sure what ecchi is, but I think isekai is when you are summoned to another world or something. How do you differentiate between the different types of anime? Is it due to how gory one is or the story?
Shounen, Seinen, Shoujo and Josei are terms for four of the main demographics that manga and anime are marketed to. Broadly:
Ultimately, the distinction between the demographics is based on which manga magazine publishes the work. The more adult genres (seinen and josei) are more likely to cover adult topics and have more explicit depictions of content such as sex and violence, but it's not an absolute thing - Fist of the North Star is much more graphic in its depiction of violence than One Punch Man, for example, but Fist is defined as shounen while OPM is seinen. Osamu Tezuka's manga series Phoenix was published across 3 or 4 different magazines that covered the shounen, seinen and shoujo demographics, although the art style and content varies a bit across them. The age and sex of the lead character can often be a hint to the demographic - it's rare for a seinen manga to have a little girl protagonist, for example - but it's not a guarantee either.
The demographics can intersect with almost all genres - there are shounen romantic comedies and shoujo horrors and josei isekai and practically every other combination if you look hard enough.
Some of the other terms you asked about are better described as genres or subgenres, and in particular:
Isekai literally means "other world" and refers to stories where a person is transported to a different world. Most commonly, a person from Earth is sent to a fantasy world, sometimes as a reincarnation, but at this point "Japanese schoolgirl dies and is reincarnated as a character in a dating simulation video game" is a rapidly growing sub-genre. "Reverse Isekai" is sometimes used to describe stories where characters from a fantasy world are pulled to Earth, but it's not quite as broadly known.
Ecchi comes from the Japanese pronunciation of the letter "H" (for "Hentai", meaning perverted, but is also a general euphemism for sex or sexual topics). Ecchi manga are ones with lots of flashes of adult content without being overly explicit with them. They're usually comedies, often rom-coms, and most frequently targeted to older teens (so they do tend to land on the border of shounen and seinen).