Worth keeping in mind that these ideologies each have multiple self-definitions (the ideal with which they describe themselves) as well as a set of definitions from the perspective of each other ideology. Tack on semantic drift (words changing meaning over time, or growing different meanings in different contexts) and it can start to feel hopelessly complicated. And they each offer different ways of understanding the world and history, so on top of all the aforementioned complexity, they also interpret historical events and real-world applications of each ideology differently. So learning about them is a process where your understanding slowly moves from abstract to concrete by getting rough definitions then tempering them with seemingly contradictory definitions, over time building a network of understanding that includes the contexts of each perspective.

My perspective is largely coming from a communist ideology fyi. But here's a quick rundown.

Capitalism is a system in which a class of owners leverage their ownership of productive assets to engage in non-equal exchange with the un-owning classes, most notably the exchange of labor value for a fraction of the products of said labor value. It necessitates a large government to enforce these hierarchies of ownership and exclusion. (Classical) liberalism is the ideology of capitalism. Conservatism is generally a subset of liberalism. It's the culturally dominant ideology now, so most of what you see and read will come from this perspective, explicitly or not.

Communism is a theoretical system in which class tensions have resolved themselves. No one knows what it'll look like, it's explicitly a theoretical ideal. Communism as an ideology is advocating for the interests of the working class against the owning class. A country that calls itself communist would probably be doing so in reference to the ideology, rather than claiming it has achieved communism.

Socialism as an ideology can be synonymous with communism, although there are subsets of liberalism that have taken on the word to mean capitalism with welfare and regulations. Socialism as a system is the interim stage between capitalism and communism, the point where workers have seized control of the state and means of production and now have a strong influence over how class tensions develop.

https://teachmecommunism.podbean.com/

https://revolutionaryleftradio.libsyn.com/

I really like these two podcasts for breaking down concepts, history, and significant figures. The second one has two spinoffs, Red Menace for individual works of theory and Guerilla History for historical events, which are both also great.

Start with reading Wikipedia articles.

This won't answer all your questions, but it will give you paths to investigate.

Some articles will be written as if you already know the subject matter, but they should give you enough stuff to keep digging.

This won't give you a degree in any of this, but it will give you plenty of puzzle pieces to build on as you see fit.

Read Socialism: Utopian and Scientific by Friedrich Engels. The quickest way to actually understand Capitalism is to work toward reading Marx's Capital with a group and other references. It might take a while to get there but this book by Engels will lay the groundwork for you to learn historical materialism and dialectical reasoning.

For Communism, read principles of Communism and the communist manifesto. But start with Socialism: Utopian & Scientific. Since communism hasn't ever existed, there have been communist groups and parties who may or may not have established different variations of socialism, there's nothing to study. You can study the history of communist parties and experiments, but there is a lot and much of it is sad or disappointing. Definitely learn about it, but its not where you should start.

Communism is a moneyless, stateless, classless society. Its a movement, something to work toward. It is not a system where the government owns everything. It isn't "authoritarianism". Its the opposite of those things.