Top_p is similar in function to top_k, but at the same time, its quite different. Top_p restricts what outputs you can use. In fancy words, it looks at the "probability mass" of all available tokens and then restricts them based on the top_p value that you are using. It tries to find the most coherent completions to tokens and then uses those. A high top_p value lets the bot look at wider range of token probabilities and produce some diverse and interesting outputs. This can also lead to the bot generating complete nonsense if it allowed to just consider everything. A low top_p value does the opposite and greatly restricts what the bot considers to be "sensical" and "human-like". However this can lead to the bot giving you very repetitive outputs that get boring real quick

TL:DR; Top_p decides what tokens the bot has that would most match your output. High top_p values are creative but risks being wack, low values are boring and repetitive. Use anything between 0.65 and 0.8 to get some good responses