Thran Portal

Land — Gate

This land enters tapped unless you control two or fewer other lands.

As this land enters, choose a basic land type.

This land is the chosen type in addition to its other types.

Mana abilities of this land cost an additional 1 life to activate.

Thran Portal will have the appropriate intrinsic mana ability for the basic land type chosen as it enters the battlefield. It is still a Gate and still has its other abilities, including the last ability, which makes the mana ability associated with its basic land type cost 1 life to activate. (2022-09-09)
You still have to pay that mana ability's other costs. Usually, this is just tapping the land. (2022-09-09)
If Thran Portal somehow gains another mana ability, that ability also costs an additional 1 life to activate. (2022-09-09)
If a land enters the battlefield as a copy of Thran Portal (as opposed to a land that is already on the battlefield becoming a copy of it), its controller gets to choose a basic land type for it and it has that type. (2022-09-09)
If a Thran Portal somehow enters the battlefield without a basic land type having been chosen for it, it does not have any mana abilities. The same is true for a land that is already on the battlefield that becomes a copy of it. (2022-09-09)
If you control more than one Thran Portal, the last ability of each of them applies only to itself. That is, controlling a second Thran Portal does not make mana abilities of all cards named Thran Portal cost an additional 2 life. (2022-09-09)