problem with using dropbox and opening files
 

hi, i got s 5 series wifi and i have one or two difficulties:

1. firstly if i have word or office files in my drop box and try to open them the error message comes up - does not know file type or something to that effect .... it works ok if it is an attachment to an email when it will proceed to view or download/upload to google docs ... how can this be resolved on the chromebook when i want to access a file either in my dropbox or if i download any file or introduce it on a memory stick?
2 where is the 'delete' button?
3 is there any way to close down all your tabs at once? rather than closing each of them one at a time ....

4 i have actived one touch to select on the keypad but it still doesnt get away with the annoying plastic click sound when i do 'eft click' on the keypad?

5 are there any good tutorials i can look up? from google or elsewhere?

6 what free chromebook apps / extensions can you recommend i try for prodcutivity and note taking / collating various urls/references i receive daily?

many thanks, sorrry for the multiple questions .... :(

Rory