If you have the need to use other libraries in projects --typescript-- not just in projects - angle - you can look for tds's (TypeScript Declaration File) that are depares and that have information of methods, types, functions, etc. , which can be used by TypeScript, usually without the need for import. declare var is the last resource
You should not use jQuery in Angular. While it is possible (see other answers for this question), it is discouraged. Why?
Angular holds an own representation of the DOM in its memory and doesn't use query-selectors (functions like document.getElementById(id)) like jQuery. Instead all the DOM-manipulation is done by Renderer2 (and Angular-directives like *ngFor and *ngIf accessing that Renderer2 in the background/framework-code). If you manipulate DOM with jQuery yourself you will sooner or later...
Run into synchronization problems and have things wrongly appearing or not disappearing at the right time from your screen
Have performance issues in more complex components, as Angular's internal DOM-representation is bound to zone.js and its change detection-mechanism - so updating the DOM manually will always block the thread your app is running on.
Have other confusing errors you don't know the origin of.
Not being able to test the application correctly (Jasmine requires you to know when elements have been rendered)
Not being able to use Angular Universal or WebWorkers
If you really want to include jQuery (for duck-taping some prototype that you will 100% definitively throw away), I recommend to at least include it in your package.json with npm install --save jquery instead of getting it from google's CDN.
TLDR: For learning how to manipulate the DOM in the Angular way please go through the official tour-of heroes tutorial first: https://angular.io/tutorial/toh-pt2 If you need to access elements higher up in the DOM hierarchy (parent or document body) or for some other reason directives like *ngIf, *ngFor, custom directives, pipes and other angular utilities like [style.background], [class.myOwnCustomClass] don't satisfy your needs, use Renderer2: https://www.concretepage.com/angular-2/angular-4-renderer2-example