My scenario,i have a SharePoint list that upon creation of a new item should send a mail to someone.(that someone is read from the TO field(user field) in the list).Can you suggest me if is possible to use Microsoft flow directly and how. OR we need SharePoint designer for it
You don't need sharepoint designer for flow. login to https://flow.microsoft.com with your O365 account.
You will need 2 Actions to fulfill your requirements (refer screenshot below)
When item is created where you select the Site Collection in which list is present and then select the list for which the flow needs to be created.
Second action is Send an Email, quite self explanatory. you can refer screenshot below. when you click in To field, you will se dynamic content on right side which are nothing but the column names from the list selected in step 1, and create the Flow.