For the most part, you determine how much time has taken place between shadowruns. if you have a deadly wound and the GM determines that it will take you a month to heal fully, then if you say that the next time you play, a month has passed, then you are fully healed. You will have to pay another month of living expenses, of course....

On rare occasions, you might participate in a multi-round event where only a short amount of time takes place between runs - anywhere from 1 minute to 1 month (usually not longer). In this case, if you end round 1 with a serious wound, then you are probably starting round 2 with the same wound...

You spend karma to train as normal. There may be instances where you might get awarded a new skill or skill level during a scenario - cherish those moments! There also may be special skills that will be unique to the campaign where you will not only have to have the required karma, but access to the trainer as well...

Items are purchased as per the book - first, you have to find someone that can get you the item (assuming that you are buying this through grey or black markets). then you determine how long it will take using the Availability ratings and how much or any extra nuyen you want to throw at it. If you want to buy something and it takes 6 weeks, then you will have to wait those 6 weeks. this means that if you are finished with one shadowrun, if you want to wait for your "toy" then at least 6 weeks (game time) must pass before your next shadowrun, which will incur another month of living expenses. This doesn't mean you can't do other runs! see below:

finish run: buy something that takes 6 weeks.
do another run after 1 week (get injured)
do another run after 2 weeks (get some cyberware installed)
do another run after 4 weeks

so, some events will cause you to wait the full time, such as surgery or healing. in this example, sometime shortly after starting the last mission, your character would be contacted by his fixer that the "toy" is ready to be picked up - you can then decide if you need to swing by during the mission, or just have him hold it for another day or two until you finish with the current run...

btw, time-wise, all SRM scenarios assume the passage of one week of game time unless the scenario states differently. From meeting with the Johnson until completion of the mission will be one week. even if the mission only takes 24 hours - the rest of the week is spent maintaining your equipment, working out, practicing and honing your skills, working/meeting with your contacts, etc.

yes - in fact, not to give much away, but if you play the first scenario, "Mission Briefing", you have the chance to gain a new contact then and there. Contacts cannot be purchased (after character creation), but will be awarded through roleplaying or other character actions...