====== Check applications listening ports ======

Run as administrator:

  netstat -a -b
  
From the output we can see that filezilla is using port 21:

  Proto  Local Address          Foreign Address        State
  TCP    0.0.0.0:21             item-ax32034:0         LISTENING
  [FileZilla Server.exe]
  TCP    0.0.0.0:135            item-ax32034:0         LISTENING
  RpcSs
  [svchost.exe]
  TCP    0.0.0.0:443            item-ax32034:0         LISTENING
  [vmware-hostd.exe]
  TCP    0.0.0.0:445            item-ax32034:0         LISTENING
  Can not obtain ownership information
  TCP    0.0.0.0:902            item-ax32034:0         LISTENING
  [vmware-authd.exe]
  TCP    0.0.0.0:912            item-ax32034:0         LISTENING

====== Check which application is using a certain port ======

From Power Shell:

  netstat -a -b | Select-String -Pattern :21 -Context 1,1
  
Output:

  Proto  Local Address          Foreign Address        State
  >   TCP    0.0.0.0:21         item-ax32034:0         LISTENING
  [FileZilla Server.exe]