Tasks like logging calls or sending e-mails are mainly managed through working with Related Lists. You can learn more about this here
In Classic view: Use related lists to display your contracts.
You will find them here: Opportunities- Klick on an opportunity (any opportunity will do)-Edit Layout- Scroll down to Related Lists.
You will also need to change the columns that are shown in the chart (see above image). The box looks like this:
Oneflow recommends the settings and order according to the image but this of course comes down to your own preference. The field that are marked as (Hidden) are not meant to be shown.
In Lightning view you must NOT use related lists as they are only customised to Classic view. Instead you make use of Components.
You find them here: Opportunities- Settings- Edit page
Opportunities vs. Accounts.
You can add the above in both the opportunities-view and the account-view.