shit

' This is your query string, exactly the same from DAS. Dont tell me you dont know DAS...
' The only difference is that this query contains '@username' and '@password'
' These you can say are placeholders for values you are going to put in the future.
' Nothing more, nothing less. They are just placeholders.
Dim myQuery as String = "SELECT * FROM Accounts WHERE Username = @username AND Password = @password"

' Create a new DataAdapter from the query and the connection, you shouldnt worry about this
' but if you want to learn more, go read the documentation about this.
da = New OleDb.OleDbDataAdapter(myQuery,con)

' Declare the command, OleDbCommand is special object that deals with the query string for you
' and does stuff like adding parameters etc. again, if you want to know more, read the docs.
' myQuery is ur query, con is the OleDbConnection object u made called 'con'
Dim cmd As New OleDbCommand(myQuery, con)

' This part is important. This is what the placeholders exist for, to be replaced.
' If you take a look into your query above, you can see there are 2 things that start with @
' followed by some name, i.e @username, @password. You have to tell VB which placeholder
' you wanna replace with what value.
' So, basically what this does, is it tries to find the placeholder in the query text (myQuery)
' that is '@username' and '@password' and replaces it with whatever value is in uservar and passvar,
' in this case 'uservar' is "John" and 'passvar' is "123"
Dim uservar As String = "John"
Dim passvar As String = "123"
cmd.Params.Add("@username", uservar) ' <- uservar is a string variable, lets say uservar is "John"
cmd.Params.Add("@password", passvar) ' <- passvar is a string variable, lets say passvar is "123"

' Open the connection
con.Open()

' OleDbDataReader is a special object as well, it is special in that it can hold data as well as change the data it holds.
' you wonder how, i shall tell u now. 'reader' is a OleDbDataReader object.
' OleDbDataReader object is special cuz the data within it is actually a single row that is returned from
' the query (myQuery) when ran to your database. So to access a column of this row, you can simply do reader(i),
' 'i' being the index of the column you want to retrieve data from. Now you're wondering, 'hmm this isnt useful if it only
' gives me back a single row, what if multiple rows is returned?'
' Well thats what the '.Read()' function is for. Its quite special in how it works. alotta special thingies here.
' Basically how it works, whenever the '.Read()' function is called, in this case 'reader.Read()',
' The function will either return a 'True' or a 'False' depending on if there is another row after the current row.
' If it is 'True', the data within OleDbDataReader object, in this case 'reader', will get replaced with the data in the next row.
' So reader will have a whole new set of data within it.
Dim reader As OleDbDataReader = cmd.ExecuteReader()

' Put it in a loop to keep reading for rows.
While reader.Read()
    ' Opens a messagebox to show the 2nd column for each row returned.
    MsgBox(reader.GetString(1))
End While