As for your initially meagre vocabulary, don't be shy about substituting an English word into your muttering—
but look up the equivalent as soon as you can. (If you have a smart speaker, their "How do you say ‘tree' in Spanish?" features are rather good.)
Keep a list of handy new words on your phone, ideally in a flashcard app. Two more tricks might help you learn more of them.
A frequency dictionary has thousands ordered not by the alphabet but how often they are actually used:
this quickly gives you the few dozen critical, functional words that glue a language together.
To enhance your vocab, Memrise is another app that uses spaced repetition to drive words home.
New ones are repeated insistently until they stick, then occasionally thereafter as reminders.
As soon as you can string a few sentences together, study in quarantine offers a consolation:
a lot of language teachers are at home, too, and only a video-call away.
For example, Sara, an Italian tutor in the Piedmont region, says her teaching hours have exploded.
Italki is a platform that links teachers and students for surprisingly low hourly rates;
casual conversation practice is especially cheap, formal instruction slightly pricier.
Find a highly rated teacher and struggle through a half-hour's conversation, shame-free.
They can use the chat function of video-call apps to write down words that elude you or that you haven't understood.
Afterwards you can add them to your flashcards.
Finally, there is reading and writing. Keeping a journal can force you to write clearly those tricky bits you've been mumbling,
making you confront half-learned material. As for reading, graphic novels are good for a realistic conversational style.
And for no-nonsense written prose, find articles in the new language on Wikipedia on a subject you know well.
Being able to guess unfamiliar terms gives a heartening sense of progress. Browser extensions can make looking up words a snap.
Just doubleclick a word with Google Translate enabled on Chrome, for example.
There is no way to learn a language without time and effort. What technology does is make that effort pay off faster.
Just remember the goal—interacting with native speakers in the flesh. You'll be out in the world again one day.