“Software” is uncountable, so you must change it to “pieces of software” Apart from that your sentence is OK in my opinion, but (at least to me) it somewhat implies that you can’t learn English well without making good use of the internet. If you want to avoid that implication you could change your sentence to: When you study English, make good use of the Internet. There are many great websites, pieces of software and applications online.

I have the app "duolingo", but I would like to find an other one

which websites and apps ?

which apps