To find and replace all occurrences of a particular text pattern in Vim, you can use the :substitute command. The basic syntax for the :substitute command is:
:%s/pattern/replacement/g
This will replace all occurrences of pattern with replacement in the current file. The % symbol specifies that the search should be performed on the entire file, and the g flag specifies that all occurrences of pattern should be replaced.
For example, to replace all occurrences of the word "apple" with the word "orange", you can use:
:%s/apple/orange/g
You can also use regular expressions in the pattern and replacement arguments. For example, to replace all occurrences of a word that begins with "a" and ends with "e", you can use:
:%s/a\w\+e/replacement/g
You can find more information about the :substitute command and regular expressions in Vim in the Vim documentation by typing :help substitute and :help pattern within Vim.