Need help with item and sitemap

First of all, I must thank all the wonderful work put behind this project. Appreciated a lot.

I am newbie to the community. I am running openhab2 on rpi2. So far I have success running hopenhab2, and controlling two zwave devices with openhab. I followed documentation to create my items and sitemap.

This is what my item looks like.

pi@raspberrypi:/etc/openhab2/items $ cat default.items
Dimmer Wall_Kitchen “KitchenWallDimmer [%.1f %%]” { channel=“zwave:device:413b45da:node3:switch_dimmer” }
Dimmer Lamp_Living “Lamp [%d %%]” { channel=“zwave:device:413b45da:node2:switch_dimmer” }

and this is what my sitemap looks like.

pi@raspberrypi:/etc/openhab2/sitemaps $ cat default.sitemap
sitemap default label=“My first sitemap”
{
Slider item=Wall_Kitchen label="KitchenWallDimmer [status %s]"
Slider item=Lamp_Living label=“Lamp [%d %%]”
}

I think I am missing something on my item and sitemap. I have few questions. I have seen some people create group and frames and their switches has “item numbers”.
I know this item and sitemap is working but Am I missing something?
How can I create group? what is frame?
Can someone share their item and sitemap file so I can compare?
Finally , I seen some youtube videos people configuring openhab.cfg file. I can not find that file on my system. (I have installed openhab from repository.)

Lastly, most confusing for me is, Both the items that I have is essentially capable of dimming the bulbs. Should I have separate sitemap lines and Item for them to be appear as “on/off” switch and as “slider” dimmer?

Sorry for such stupid questions.

Any answer will be appreciated.
Thanks.

For information about groups please have a look at http://docs.openhab.org/configuration/items.html#groups
and for frames http://docs.openhab.org/configuration/sitemaps.html#element-types.

Frame [label="<labelname>"] [icon="<icon>"] {
        [additional sitemap elements]
}
Group  All
Group  gSensor             (All)
Group  gTemperature        (gSensor)

Number  Sensor_Temperature  "The Temperature is [%.1f °C]"  <temperature>  (gTemperature)  {knx="1/0/15+0/0/15"}

In openhab2, such a openhab.cfg file does NOT exist anymore. OH2 Bindings are typically configured through PaperUI, as is the system.
When looking in older posts, you will need to watch out very carefully for the version, it can be confusing, but there have been numerous changes some subtle, others more massive in OH2. The links that have been posted above are essential, read it all and more than once.