Train travel in Britain

Janice, I believe at the first station, prior to your first train trip, you need to present your rail pass and an ID (passport) to a ticket agent to validate your flexpass. It is then that your particular plan (X travel days in Y days) begins. The pass does not guarantee you seat on any particular train. It only substitutes for having to purchase a ticket. If there is a particularly long voyage during your trip or a frequently crowded one, you could pay additional for a seat reservation. (I did that recently going from Edinburgh to London, just for the comfort of knowing our two seats together were waiting for us.) For most short trips, and it seems you may have a few, you just look for an unoccupied seat and take it. When reservations are available there are often little digital displays above the seats indicating if and between which stations a seat is reserved . I failed to notice them initially and took someone's reserved seat by mistake. If it happens, just apologize and move to another seat. Ask for help from any train employee whenever you are concerned. My own experience has been that UK rail workers from station agents to conductors to men and women working on the tracks have all been invariably nice when I approached them for help.
Happy travels

Don't be nervous! I think that with a 1st class pass, you should be OK. There are special dedicated 1st class carriages and they are often uncrowded. Matt's advice sounds good.
Maybe you could post this on the Transport section? There are some very knowledgable people there.

Is my pass good for city buses or just train travel from city to city?

Your pass is not good on city buses, nor on local 'metros', the Tube/underground, etc. And you've been given correct instructions about getting your pass validated. You wil also need to enter the date on each day you travel- DO NOT DO THIS AHEAD OF TIME. Do it after you board the train the first time on a given day. We have never made reservations and always found a seat except on a couple of sections on a few trips. These were on 'regional' trains with only one or two cars and no dedicated first class service. Each time seats opened up at the next station, so we only had to stand for a few minuets.

All good advice. Do be sure to write in the day of travel each day you wish to use a day of your pass. Don't do it on a previous day but you must do it just before or right at the beginning of your train journey. If the station has manned barriers (ticket gates) you need to show the pass to the person manning the gate (sometimes behind the window with an electrical release of the gate) and the correct date needs to already be on the pass or they won't let you through. If the conductor checks your pass before you have written the correct day in the box you are liable for them to cross out a day (you lose the day) and then they will write the correct day in the next box. You must have it written in before they get to you.