Problem after installing Prestashop

Hello everyone , i have a problem with prestashop in my server ,
first of all i have install the cyber panel on my Linux ubuntu18
after that i installed the last version of prestashop on it
everything was going fine to the end i have this problem :
my website is always unsecure knowing that i have added ssl

• the back end admin page does not work fine for example if i click on Advanced parameter → performance it automatically logged out and ask for the username and password again
• the front end at the beginning did not work and always showed 404 no page found after that it is going to work but unsecure
  what should i do ?

Could it be that you installed the shop without SSL? Is this always redirecting you to the version without https and therefore the sessions do not work?