Same as the MS Outlook, you can manage your tasks in Gmail. If you add the time to the task, you can also view the task in Google Calendar.
Step 1: Login your Gmail account (please refer here to open one if you do not have an account yet);
Step 2: On the right panel of your Gmail account, click the "Tasks" icon;
Step 3: Click the "Add a task" icon;
Step 4: Type the task title, e.g., "Lunch with friend";
Step 5: To edit the task, move the cursor on the task and click the "Edit" button;
Step 6: Change the title or add the time in the new window, click the left arrow on the top-left when you finish;
Step 7: Check the circle in front of the task to "Mark complete".