How can I correctly generate and use the shopApiKey in Shopify SDK for mobile integration?

[Silverberry]

I am looking for shopApiKey

shopDomain and shopApiKey both are required to pass the value in shopify sdk for mobile integration. 

There are two queries, 

1) From where exactly this api key can be generated from the shopify panel /

2) I was able to generate api key, but not sure if its the correct one, 

whenever I am passing the key value in url,  it gives me an error HTTP 403 forbidden error 

url : gid://shopify/ProductVariant/"+packageId

graphClient = GraphClient.builder(context)
.shopDomain(shopDomain)//BuildConfig.SHOP_DOMAIN
.accessToken(apiKey)//BuildConfig.API_KEY
.httpCache(new File(context.getCacheDir(), "/http"), 10 1024 1024)
.defaultHttpCachePolicy(HttpCachePolicy.CACHE_FIRST.expireAfter(5, TimeUnit.MINUTES))
.build();

Need Shop API key to pass value 

.shopDomain(shopDomain)//BuildConfig.SHOP_DOMAIN
.accessToken(apiKey)//BuildConfig.API_KEY

I am following below article but its not that helpful. 

https://www.shopify.in/partners/blog/shopify-android-buy-sdk

Can anyone help me out ?