A font from the Google Fonts library goes on an individual block, on top of the template's font. It's available on every plan and costs no credits.
Select a text block
Click a heading, a paragraph or a list. On the right, in the “Text” section, click the font field — it shows the current font. To change the font of several blocks at once, select them together: the panel shows a “Fonts” section.
Open the “Google Fonts” tab
The list has two tabs: “Built-in” and “Google Fonts”. The second one holds over a thousand families. Search by name in “Find a font”, or pick a category instead of “All categories”: “Sans”, “Serif”, “Display”, “Handwritten”, “Monospace”.
The “Cyrillic” checkbox keeps only fonts with Cyrillic letters; it's on by default in Russian and Ukrainian presentations.
Pick a font
Click its name — “Loading…” appears next to it, and the font goes on the block. Pick the weight in the field under the font.
Go back to the template font
To make the block follow the template again, open the “Built-in” tab and pick the first line — the font marked “template”.
The font is copied to us when you pick it, so viewers of the presentation never connect to Google. In a PowerPoint file, a Google font shows only if it's installed on the computer — more on that.