I was in Lisbon in late May on the Rick Steves Best of Portugal tour. I was there 3 days before the tour began and rode the Metro, a tram, a funicular, and buses...and paid for all using the Viva Viagem card. I found buying a Viva Viagem card very easy. The cost per ride seemed to be less than what I've paid on the London Underground.
Before I left the US, I watched some YouTube videos on the Lisbon Metro that included directions on both buying and adding money to an existing Via Viagem card. As best I remember, when you first buy the card from the ticket machine, you touch the prompt for English, then the machine asks if you already have a Via Viagem card (answer no). You'll be charged a small non-refundable amount for the card. Then you are asked whether you want to buy a certain number of rides or instead load a fixed amount onto the card. I chose to load a fixed amount.
I chose not to buy a Lisbon card because admission to some sites would be paid for by the tour. But, I was very surprised at how inexpensive admission to the Coach Museum (Belem) and the Tile Museum were, given I am over age 65. So...the Lisbon Card may or may not be worth the money.
Whether you buy the Viva Viagem or the Lisbon Card, be careful not to bend it.