When you are inside an activity and need to go to a fragment use below
getFragmentManager().beginTransaction().replace(R.id.*TO_BE_REPLACED_LAYOUT_ID*, new tasks()).commit();
But when you are inside a fragment and need to go to a fragment then just add a getActivity().
before, so it would become
getActivity().getFragmentManager().beginTransaction().replace(R.id.*TO_BE_REPLACED_LAYOUT_ID*, new tasks()).commit();
as simple as that.
The *TO_BE_REPLACED_LAYOUT_ID*
can be the entire page of activity or a part of it, just make sure to put an id to the layout to be replaced. It is general practice to put the replaceable layout in a FrameLayout
.