You are a developer starting out on your IT journey, you will be learning frameworks, languages and tools that will allow you to earn money in order to obtain the tools you need to get more money and StackOverflow fame.
A developer level refers to your calibre as a developer, every time you complete a session (different sessions give different XP), XP is added to your player which contributes to his developer level. This is different to XP and Levels in languages/frameworks/tools as this refers to the developers skill as a whole.
Starting off you will select a language to begin with, once a learning session for a language completes you earn XP for said language which contributes to your level in said language. XP for a language will allow you to "buy" other frameworks and languages to learn. Upon reaching a certain level in a language, you may fulfill requirements for a job, which will allow you to earn in game currency. The higher your level in a language, the faster learning sessions are for that language and related languages/frameworks/tools. Languages alone will not provide many job oppurtunites, but will get you started off.
Frameworks are similar to languages, however these provide many more job oppurtunites, and also allow you to build your own projects, which may be another source of income. Learning related frameworks and tools for a language will also increase the speed of XP, and increase your calibre as a developer.
Tools are developer tools that aid in development and also provide XP towards your overall calibre as a developer, tools to learn can also be purchased from the shop (eg: IntelliJ Ultimate, Adobe Products)
The levels you can be at in a certain framework/language/tool are divided into sections, reflecting your skill in said framework/language/tool. These sections are letter based, ranging as F - E - D - C - B - A - S - S+ - S++ - Z Your skill level will also translate into the job oppurtunites you have, junior dev, senior dev, etc.
Jobs are unlocked when you have reached a certain level in what you are learning, allowing you to gain in game currency through a job session, which is similar to a learning session, except that it gets you money but less XP than a learning session. Jobs can be working at a company, Freelancing, Youtubing, Blogging, etc.
Projects are coding projects that you create on ypour own based on your skill set, you can make money off of these and use them as a secondary income source. Projects are also a way of creating your own items, similar to crafting, you could build a robot and code it through an arduino/components bought in the shop, a discord bot, build and code a keyboard, etc. Projects are a central aspect of the game, equivalent to crafting.
Items are things you can buy from the shop using in game currency, these can be hardware components (Computer Components, Peripherals, Chipsets, etc.), proprietary software tools (IDEs, Subscriptions, etc), Computing Books (Increase Level), Furniture, etc. Tools that you buy will be treated as software tools, and as such will also have learning sessions for them. Items are divided into rarities, namely: Common, Uncommon, Rare, Epic, Legendary, Mythical, Ancient, Forbidden, and they also may have modifiers on them.
A session is a core component of this game, it can be a learning session that results in XP for a language/framework/tool or a job session that results in money being earned. Multiple sessions can be held at once, tapping on the session buttons will speed up their progress, all sessions automatically restart once finish.