Several reliable methods exist:
Go to translate.google.com, enter English text, select Sinhala as target, click Translate.
Use Bing Translator or the Microsoft Translator app; same process.
Print or online English-Sinhala dictionaries (e.g., Madura English-Sinhala Dictionary) for word-level lookup.
For accuracy, nuance, and certified documents, hire a qualified translator via platforms like ProZ, Upwork, or local agencies.
Machine tools are fine for gist; humans are essential for formal, legal, or literary content.