How can I install or download Adobe Experience Manager?
AEM is a licensed product. You can reach out to Adobe's sales team using this link https://www.adobe.com/request-consultation/experience-cloud.html.
As @ArpitVarshney mentioned AEM is License Product.
Its Not possible to download like we do for wordpress,Drupal and other CMS tools. You have to contact Adobe team to buy it.
The best way to work on it, is the organisation where you work they might have the same with license. Ask them and explore the AEM. But dont use outside organisation.