i assume we have a dll of our Ssis Custom task. in my other post, i have already share "how to create a SSIS custom task very easily".

assume our DLL name is : TestTask.dll

now follow the below 3 steps: [see below Image for help]

1. install the dll in GAC 
2. copy the dll to SSIS DTS location
3. Test the Task is working

1. install the dll in GAC (see image)

• find the GACUtill in the "Microsoft SDKs" folder... in my case it is in "C:\Program Files (x86)\Microsoft SDKs\Windows\v7.0A\Bin\gacutil.exe"
• if you dont have it installed .. you can download it from here (click here).
• open Command Prompt as Administrator
• now execute below
• "C:\Program Files (x86)\Microsoft SDKs\Windows\v7.0A\Bin\gacutil.exe" -if "C:\TestProj\bin\Debug\Test_Task.dll"

• now find your Microsoft SQL Server location and go to DTS\Task folder
• in my case it is in "C:\Program Files (x86)\Microsoft SQL Server\100\DTS\Tasks"
• the folder "100" may vary due to sql server version.
• now copy the dll and past it to the Tasks folder, you may need administrator permission.

• open the Visual Studio.
• close it of already open then open it again.
• create/open a SSIS project 
• now look at the tool box.
• if the task is already there then we are done
• if the Task is not in there then follow below
• right click on ToolBox, then click on "Chose Item".
• OR click "Tools" menue -> click "Chose ToolBox Items..."
• a new window will come with all of the Installed tasks..
• go to "SSIS Control Flow Items" [in general all goes to this location]
• select/check your Task(HelloWorld)
• click ok