Angular - adding a material.module.ts to build

I would like to add the Material Design Components to my angular 9 project to make my life a bit easier.

I added it to my application and then got the following as an error for some existing code (when I realised I had to install @angular/material)

    ERROR in src/app/app.module.ts:4:81 - error TS2306: File 'C:/Workspace/....../node_modules/@angular/material/index.d.ts' is not a module.

    4 import { MatInputModule, MatButtonModule, MatSelectModule, MatIconModule } from '[b]@angular/material[/b]';

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I looked around, and found the following

https://stackoverflow.com/questions/58594311/angular-material-index-d-ts-is-not-a-module

So it seems that adding angular material to angular 9 has had issues.  I tried to follow what the person with the most upvotes had done, but I don't know how he has integrated material.module.ts into the project.

I created a file in the source folder called material.module.ts with the contents he posted and then referenced this in the app.module.ts.  However this came back with the following:

    ERROR in src/app/app.module.ts:49:5 - error NG6001: The class 'MaterialModule' is listed in the declarations of the NgModule 'AppModule', but is not a directive, a component, or a pipe. Either remove it from the NgModule's declarations, or add an appropriate Angular decorator.

    49     MaterialModule
           ~~~~~~~~~~~~~~

      src/app/material.module.ts:115:14
        115 export class MaterialModule {
                         ~~~~~~~~~~~~~~
        'MaterialModule' is declared here.

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What do I do to integrate this file into my application, do I have to generate a component or do I have to add a decorator (what's that?)

Thanks