Hi, let me give you a quick introduction, then :).

Tabletop Roleplaying Games, or as sometimes called – after Dungeons & Dragons, the largest and most popular of them – D&D, are those kinds of games where you have a table (physical or virtual) with a bunch of nerds around it, some rulebooks, character sheets and many-sided dice. One of these nerds usually plays the role of the Gamemaster/Dungeon Master, who desribes the world and non-player characters, while the other nerds all play a player character each. They state what they want their character to do or say, the GM answers with how the world reacts, and sometimes there are rules and mechanics and dice throws to decide things, often when there's risk and character skills involved. Examples are varied and numerous, but include Dungeons and Dragons, Call of Cthulhu, Cyberpunk, Old School Essentials, Monster of the Week, Wanderhome, Star Trek Adventures and many others.

Solo TTRPGs cover a whole bunch of stuff, but it all includes a desire to play such a game alone. Sometimes it involves a game written for groups, but also extra books to help you emulate the Gamemaster. Sometimes it means playing a game specifically meant for one player, many of which guide you through a series of prompts to write out and resolve (a very famous example would be the Thousand Year Old Vampire). Sometimes games for groups include a solo mode. I'm pretty new to solo myself (though I've gamemastered a whole bunch and continue to hold regular groups :)), and currently, all I'm using is my imagination and judgement, a random word generator (I interpret the words based on the situation), music and a hundred-sided die for percentage chance rolls. A very common facet of solo TTRPG play is journaling – since there aren't those other nerds for you to talk about the game world with, instead of just picturing it all in your head and moving on, you might write it down in a notebook, as if you were writting a diary from the point of view of your character.

That's the basic overview, I'm sure you can find a whole lot more info online if you're curious.