蒙古袍女装生活装:帮忙解释一些VB程序

实在是看不懂啊，哪位好心人帮帮忙啊

Public Function ExecuteSQL(ByVal sql As String) As ADODB.Recordset
Dim mycon As ADODB.Connection
Dim rst As ADODB.Recordset
Set mycon = New ADODB.Connection
mycon.ConnectionString = connstring
mycon.Open
Dim stokens() As String
On Error GoTo exectuesql_error
stokens = Split(sql)
If InStr("INSER,DELETE,UPDATE", UCase(stokens(0))) Then
mycon.Execute sql
Else
Set rst = New ADODB.Recordset
rst.Open Trim(sql), mycon, adOpenKeyset, adLockOptimistic
Set ExecuteSQL = rst
End If
exectuesql_exit:
Set rst = Nothing
Set mycon = Nothing
Exit Function
exectuesql_error:
Resume exectuesql_exit
End Function

Public Function connstring() As String
connstring = "provider=Microsoft.Jet.OLEDB.4.0;Data source =" & App.Path & "/xs.mdb"

End Function

Public Function Executeqx(ByVal txt As Integer) As String
Dim sql As String
Dim mycon As ADODB.Connection
Dim rst As ADODB.Recordset
Set mycon = New ADODB.Connection
mycon.ConnectionString = connstring
mycon.Open
Set rst = New ADODB.Recordset
sql = "select admin from use where username='" & username & "'"
rst.Open Trim(sql), mycon, adOpenKeyset, adLockOptimistic
If rst.EOF = True Then
MsgBox "非法用户！", vbExclamation + vbOKOnly, "警告"
Executeqx = "nothing"
Exit Function
End If
If rst.Fields(0) = "y" Then
Executeqx = "admin"
Exit Function
End If
rst.Close
sql = "select readonly from use where username='" & username & "'"
rst.Open Trim(sql), mycon, adOpenKeyset, adLockOptimistic
If rst.Fields(0) = "y" Then
Executeqx = "readonly"
Exit Function
End If
Select Case txt
Case 1
sql = "select qx1 from use where username='" & username & "'"
Case 2
sql = "select qx2 from use where username='" & username & "'"
Case 3
sql = "select qx3 from use where username='" & username & "'"
Case 4
sql = "select qx4 from use where username='" & username & "'"
End Select
On Error GoTo exectuesql_error

Set rst = New ADODB.Recordset
rst.Open Trim(sql), mycon, adOpenKeyset, adLockOptimistic
If rst.Fields(0) = "y" Then
Executeqx = "true"
Else
Executeqx = "false"
End If
exectuesql_exit:
Set rst = Nothing
Set mycon = Nothing
Exit Function
exectuesql_error:
Resume exectuesql_exit

End Function
我知道是与ACCESS数据库有关的一段代码
就是看不懂都是什么意思啊
比如On Error GoTo exectuesql_error 什么含义啊？
唉，头痛啊
请大家帮忙，明白哪句就给解释一下
谢谢啦

On Error GoTo exectuesql_error
stokens = Split(sql)
If InStr("INSER,DELETE,UPDATE", UCase(stokens(0))) Then
mycon.Execute sql
Else
Set rst = New ADODB.Recordset
rst.Open Trim(sql), mycon, adOpenKeyset, adLockOptimistic
Set ExecuteSQL = rst
End If
exectuesql_exit:
Set rst = Nothing
Set mycon = Nothing
Exit Function
exectuesql_error:
Resume exectuesql_exit
这段不太明白了