The www.(yourdomain.com)/wp-admin lets you login to the WordPress Dashboard. There is a Help link at top right of screen.

To edit web pages select Pages >> select page from list >> Edit

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Edit the page in WYSIWYG screen. Then click Update button on right.

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To change information that shows on all pages, e.g. on the Side-bar or foot of all pages, select Appearance >> Widgets >> the widget in right hand column, then edit that.