OK. Go ahead and post an introduction in the game thread. I need to know where Otter is in the car and (in brief) what she has on her.
The train's host has a rating of 4. This means its attributes are going to be 4, 5, 6, and 7. Otter doesn't know for sure which attributes have which scores but it's likely to have a high Data Processing and Firewall with low Attack and Sleaze. The host is currently running a single Patrol IC, which hasn't yet spotted Otter (it's making a Perception check every 1d6 rounds, as described on page 86 of Data Trails). Even if the host hasn't noticed anything wrong yet it's going to be alerted at any moment by outside forces so Otter should expect more Patrol IC incoming. They will find her, given time. An investigating spider will accelerate that.
To send a message through the Matrix you'd use the aptly-named Send Message action, described on page 242. You can send text, audio (don't ask how - just run with it!), images, and other files. You can communicate with your team more-or-less as if you were using a comm normally, except for the increased time it takes - one of the weaknesses of being in a different plane of existence I guess. The recipients will need to have their comms turned on with a SIN plugged in, though of course they can be running silent.
To search for information you'd use the Matrix Search or Matrix Perception actions, described on page 241. The book says that a Matrix Search in a host always takes 1 minute, which is of course absolutely bananas in situations like this. We'll have it take a complex action, like Matrix Perception, with a threshold to be determined based on the general availability of the information. I'll use the longer time requirement if you're ever snooping for super secret stuff in a megacorporation's host. A Matrix Search will not show you where a specific icon is. Matrix Perception will let you find the icons (for example - Otter's got marks on the icons controlling pathing and speed). So, as another example, if you used Perception to find the emergency brake icon you could immediately hack it and activate it, but without the Search you wouldn't find out under what conditions it might activate on its own.
I'll be making the rolls using an online roller. You can feel free to suggest dice pools when you're describing what actions you're taking but I'll be making the actual rolls. I know it's not the most efficient way of doing it - sorry! I have no problem using a roller that would allow me to make player roll logs accessible to you guys.