You can open and pay into one each type of the different ISAs available per tax year.

For example, I can open EACH of the below accounts within a tax year and pay into them each concurrently (currently I have a H2B + LISA opened in the 19 - 20 tax year).

The types are:
Cash ISA - The Help to Buy (H2B) comes under this type

Lifetime Isa (LISA)

Stocks & Shares ISA (S&S)

Innovative finance ISAs - P2P lending, crowdfunding, lending to businesses etc.

This article provides a great summary beyond what I have shared here.

https://www.moneysavingexpert.com/savings/ISA-guide-savings-without-tax/