It is interesting that you are keen to learn Sanskrit, language of Vedas, one of the oldest, classical literatures. It has been one of the official languages in India though not widely spoken but used in religious occasions/chanting in temples.
Below are a few online dictionaries for your references.
There have been free as well as paid classes/lessons in the online platform.
I have listed here some free online platforms that teach Sanskrit for beginners.
1.https://www.learnsanskrit.org/ offering free as well as paid beginner-friendly lessons in a simplified manner through Skype.
2.https://www.thesanskritlanguage.com. This online platform is designed by Walter Harding Maurer with guidance from the textbook, "The Sanskrit Language" written by him. The book can be bought from Amazon for desiring consistent learners.
3.https://www.apnacourse.com. Offered by Vyoma Linguistic Labs Foundation, the course contains free standard plan for beginners and paid enterprise plan for multiple participants.
4.https://www.enjoylearningsanskrit.com. This is available as a mobile app as well and with this tool you can study the language by yourself.
5.https://www.acharya.gen.in/ teaches basic lessons in Sanskrit through self-study with the guidance of online dictionary.
6.https://www.sanskrit.today/ is an online portal that enables the learners to interact with others and with free as well as paid set of curriculums organizing events and forum sessions locally too.
7.https://www.arshakulam.org/ It is an NGO that conducts online classes through Zoom app for learning Vedanta and Sanskrit.
Other than the above-mentioned e-platforms, Chinmaya International Foundation offers two types of Sanskrit courses, one for beginners and the advanced course for others but under paid programs.
Learning Sanskrit with abundant resources available online would be rewarding as such and I wish you all the best to get go.