Build an Online Store

Fresh installation of opencart is giving the following error: Warning: mysqli::__construct(): Headers and client library minor version mismatch. Headers:100023 Library:100106 in /home/raimksqg/public_html/system/library/db/[login to view URL] on line 7 Warning: session_start(): Cannot send session cookie - headers already sent by (output started at /home/raimksqg/public_html/system/library/db/[login to view URL]) in /home/raimksqg/public_html/system/library/[login to view URL] on line 38 Warning: session_start(): Cannot send session cache limiter - headers already sent (output started at /home/raimksqg/public_html/system/library/db/[login to view URL]) in /home/raimksqg/public_html/system/library/[login to view URL] on line 38 Warning: Cannot modify header information - headers already sent by (output started at /home/raimksqg/public_html/system/library/db/[login to view URL]) in /home/raimksqg/public_html/catalog/controller/startup/[login to view URL] on line 71 Warning: Cannot modify header information - headers already sent by (output started at /home/raimksqg/public_html/system/library/db/[login to view URL]) in /home/raimksqg/public_html/catalog/controller/startup/[login to view URL] on line 131 Need to figure out why. Then need to Install Opencart with and a theme I purchased from Evanto Market. ([login to view URL])