Check out example codes for "Could not find a declaration file for module 'react'". It will help you in understanding the concepts better.

Code Example 1

//First try  ( works for most of the cases) 
npm install @types/module-name

//if that does not solve your problem than . (will surely solve your problem)

Inside the project create a folder called @types and added it to 
tsconfig.json for find all required types from it . So it looks somewhat 
like this -

  "typeRoots": [
            "../node_modules/@types",
            "../@types"
        ]
        
And inside @types folder create a file called alltypes.d.ts .To find the unknown 
types from it . so for me these were the unknown types and I added it over there.

declare module 'react';
declate module 'react-dom' ;

So now the typescript didn't complain about the types not found anymore .

Code Example 2

yarn add eslint-import-resolver-typescript -D

// Add in .eslintrc
"settings": {
        "import/resolver": {
            "typescript": {}
        }
    }

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