You have downloaded the Oracle 12c archives (zipped files) from Oracle.com
and now you need to extract it to start the installation and this is important, because most people extract to wrong destinations and get the errors during installation and the errors could be related to missing files or installation get stucked in between.
So here I will tell you for proper extraction location for installation archives, please check the following:
Suppose you have the following archives for Oracle 12c database installations:
Then extract the first archive into any folder and the following folder would be created:
Then extract the second archive and your archive program may suggest you the default folder winx64_12102_database_2of2 for extraction but you change it to winx64_12102_database_1of2 means with the name of your folder in which you have extracted the first archive or the better way is to copy the whole path of first extraction folder and then paste for extraction location, for example if you have extracted first archive to "D:Softwarewinx64_12102_database_1of2" then copy this whole path and then specify it for second archive file extraction.
After that start the installation by running setup.exe located in winx64_12102_database_1of2database folder.