First, familiarize yourself with the options available in the Downtime Activities thread.
1. Choose your lifestyle. Choose your lifestyle from the available options: squalid, poor, modest, comfortable, wealthy, or aristocratic. Then, pay your lifestyle costs upfront for the downtime period. For example, if you choose a modest lifestyle for your character and you have 1 week of downtime, that will cost 1gp x 7 days = 7gp to be paid up front. You may change your lifestyle, but you can only go up one step from your current lifestyle each week (it takes time to climb the social ladder!). On your first downtime session you can start wherever you like on the scale.
2. Choose how you are spending your downtime. Decide what activities you want to spend your downtime on. You can mix-and-match activities if you have enough time to do more than one. You can roll on the tables for that activity, but these are meant to be DM-facing rules so sometimes they won't apply or will be slightly modified, depending on the circumstances. We will work together to figure it out!
3. Resolve Downtime Activity. This may involve paying associated costs, making skill checks, and rolling on tables. Rolling can be done in this thread. Ask for advice if you aren't sure how it works!
4. Resolve other tasks. Some tasks don't require an entire downtime system to resolve. This might include shopping for mundane gear or roleplaying-only activities like taking care of a family. You can narrate these activities if you feel it is appropriate and spending money on related costs at the end of the downtime session.
5. Write up the story. Make a post that summarizes what went down for the duration of the downtime session. You can make it as simple as you want, but you can also embellish it with narrative descriptions of how things turned out. It can be in character or out of character, your choice.