Spending Karma
Level advancement costs Karma equal to your new Level. Going from Level 1 to Level 2 costs 2 Karma. Level 2 to Level 3 costs 3 Karma, and so on. You must be Rested and completely healed from all Injury before you can increase your Level.
Everything else that costs Karma requires Karma equal to its current rating to advance. A Role at Rank 2 costs 2 Karma to advance to Rank 3. No ability can exceed your current Level - that's your absolute ceiling. Maneuvers can't exceed the Role on which they are based.
By default, you can only increase one score per session, and only at the end… but if you're playing a short campaign, advance when it makes sense. If the group settles into a down time period, the GM can call everything before that session and allow advancements, then start a new session, so long as the PCs are Healed and Rested. Characters can't keep more Karma than the cost of their next Level. It's ok to receive more than you can keep, as long as you spend it before the next session.
You can spend Karma as emergency luck. When you want a Luck Token but can't spend one, such as in downtime between sessions, use actual Karma instead. As a last-ditch effort, if you absolutely can't succeed any other way on a vitally important roll during a session, use a Karma to Succeed, even when a Token wouldn't be enough. When the PC has spent every other resource and is about to fall to their absolute doom in the bottomless ravine, a Karma will let them catch the edge by their fingertips and crawl out before collapsing.
Sometimes it's good to have a little Karma on your side.