For your first question, Ivan F. Moala has that information right here...
http://xcelfiles.homestead.com/VB_Quick17.html
As for your second question, this will do ya:
Sub duhChecker()
Dim ws As Worksheet, sht As String
For Each ws In ThisWorkbook.Worksheets
ws.Activate
If [A1].Value = "50" Then GoTo nextSht1
'other code here
Next ws
MsgBox "Nope"
Exit Sub
nextSht1:
sht = ActiveSheet.Name
MsgBox sht
'do stuff if 50 is found
End Sub
This will work for whatever your sheet name is, and however many sheets you have. Just take out the msgbox sht part and replace the 'do stuff if 50 is found with whatever code you want. The msgbox was for testing purposes only.
The big caveat with this code is (and I'm not sure how you want to handle it) is if there is 50 in multiple sheets, this code will stop at the first value found. So if there is 50 in A1 of more than one sheet, and you want to do something for those, this will need to change.