If you are a total new in Shopify, please head up to Overview with Shopify section which contains basic steps of Shopify.

Go to Customize page > Theme Settings > TYPOGRAPHY
Typography Settings
Go to Customize page > Theme Settings > COLOR
Colors Settings
Go to Customize page > Theme Settings > Currency
Currency Settings
Go to Customize page > Theme Settings > Custom CSS
Custom CSS Settings
Go to Customize page > Theme Settings > Search Behaviour/strong>
Search Behavior Settings
Go to Customize page > Theme Settings > Logo > Favicon Image
Favicon Settings->You can change header announcementbar settings from here.left text, right text, left link etc. all detail change here.
->You can change section height, announcement menu, also change announcementbar background image frome here.
You can change header detail like header height, change logo, logo width, category menu and category menu width change here.
You can change menu here , menu type like mega menu or navigation menu , enable or disable sticky header, enable breadcrumb, spacing setting also available.