Estibot is a good quick tool to get a slight idea of the possible potential for what a domain may sell for if you can find the right buyer. But the sales price could be much lower or higher as was said.
If you want to see how well Estibot works, go to DNJournal.com or another site that publishes what domains have sold for. Put those domains into Estibot and see what comes out.
And your English is not bad at all, but if you are not 100% comfortable with English you should be extra careful with the domains you buy. There are somethings that I see people do a lot that are not correct US English. For example I would never use the word "softwares" because the sigular and plural versions of the word are the same, "software".