David-A

Yes. Very, very easy.

I'll describe how to get to the ones I mentioned as I could do it blindfolded.
[So that is the store that Tesco call "Feltham Dukes Green" and the Asda next to feltham station.

The 285 bus stops right outside your hotel.
To head to the stores I mentioned you want the stop on your side of the road.

- If you have a pay-as-you-go oyster card, then each journey will debit £1.30 unless you have already hit the daily maximum charge, in which case it will cost nothing.
- If paying cash, each journey will cost £2.20!
- If you have a paper 'travelcard', then these journeys stay within the covered area (some london busses do head outside the area covered by the travelcards). so if you have a travelcard it should cover it.
http://www.tfl.gov.uk/tickets/14415.aspx

Stick your arm out to stop the bus in plenty of time for the driver to see it.

You can get a timetable here:
http://www.tfl.gov.uk/gettingaround/4867.aspx

Stick 285 into the route number box midway down the page.
Select "Towards Kingston" (The 285 runs between Kingston and Heathrow, you want to head away form heathrow)
Click on the stop you are starting from to get a timetable from there. Your stop should be "New Road / Bath Road"
This will give you a link to a PDF file showing the journey time in minutes to the later stops in the top half.
In the bottom half will be the departure times from that stop - when the bus should come by.

This is a 24 hour route, so the worst it should be is every 30 minutes in the dead of night. But, during peak traffic times the busses can get bunched up due to delays, and you might find a service supposed to run every 10-15 minutes has a gap of 40 minutes and then three buses within 5 minutes, etc.

If you go here, you can stick in the bus route 285 and see the route:
http://www.tfl.gov.uk/tfl/gettingaround/maps/buses/

The bus takes a detour into Feltham station forecourt.
The ASDA is located close to the train station, you can see its sign from the station. (from the bus stops walk accross the level crossing to cross the train tracks (when the barriers are up) walk along the short road to the Mcdonalds, turn right onto Feltham high street, walk along the highstreet until the entrance to the asda is visble on a pathway to the right.

The Tesco is an earlier stop. I think the stop is called "Central Way" - the bus should have a display and automated voice announcing the stops, but not always and may be broken (occasionally it may be really broken and displaying incorrect info for another route, so check it seems to make sense as you go.)
The tesco will be on the right hand side, so sit where you can see out.

To stop the bus, you push one of the bell buttons in advance of your stop.
If you are not sure, tell the driver where you want to go, and they will often try to remember to stop.

[Generally you exit a bus through the doors on the side in the middle/towards the rear, but you board near the front. Espeically when there is a queue of people to board at the stop you are getting off.]

The tesco will be on the opposite side of the road from the bus stop, so cross at the crossing. The return bus stop is right outside Tesco.

Due to the big central reservation on bath road where your hotel is, coming back you will have to get off earlier to use the crossings at the big junction called "harlington corner". Because of this, you could just as easily get back the "90" bus, goes from the tesco to the same stop (but it then continues towards hayes and harlington station, not along bath road).

For the feltham asda, either take the 285 back from feltham station or the 90 from feltham high street (which will be apparant when you are there).
Note, at feltham station the two stops for the 285 in different directions (you want the one towards heathrow).