I want to explain it in simple steps,
step1:
go to: http://vote.liquideos.com/
step2:
download EOS voting tool(I used windows version)
step3:
unzip the folder and open the application, remember it wont share your private keys
step4:
once the application loaded, click on next.
step5:
select the desired block producers, there is a search option in the tool.
step6:
submit you private keys and click on vote. thats it its done.
step7:
you can verify you voting on blockexplorer also.
http://eosflare.io/