"I founded a club myself."
Translation:Ich habe selber einen Club gegründet.
I'm not a native speaker, but from what I've seen online, there is no difference and both should be accepted. The only difference I could find online was that "selbst" was once considered more formal/elegant than "selber", and that in some sentences "selber" may be chosen because "selbst" could get confused with its other meaning of "even". Maybe a native speaker can enlighten us further.
Finden means to find something that was lost. If you lost your glasses and then found them, you could say "Ich habe meine Brille gefunden". Found as in created though, gründen must be used. If you founded a club, company, or a musical group, it would be "Ich habe (eine Gruppe, eine Firma, usw.) gegründen".