Question: I am new in Alexa skill kit development   

I have already read Tutorials on Alexa Skill Kit   

I have to implement Alexa Skill , In which I need to manually send command and want Alexa to speak it.

i.e When user login in system I can fire API as Alexa request and I want Alexa device to Speak that for example "Welcome Have a great day"

Is it Possible ? Or Any other alternatives. ?

Answer: 
Notifications for Alexa skill are in still in beta. You can apply for the access to it by filling up this form here : <https://alexa.au1.qualtrics.com/jfe/form/SV_72lplGGegxNZ9Ln>
I think you may want to use proactive events for your skill. They are now commercially available. You will be able to send a notification to your skill and the Amazon device will blink (yellow). However you will still need to say "Alexa check my notifications" to retrieve the actual message

<https://developer.amazon.com/docs/smapi/proactive-events-api.html>

Another idea would be to use "progressive response" feature: <https://developer.amazon.com/docs/custom-skills/send-the-user-a-progressive-response.html>

You can fire the interaction to alexa when your API is invoked and send a progressive response. Not really a notification but it might serve you. This way you will not need to ask to check the notifications to Alexa but directly get the voice message in the progressive responses