You can often reuse the textures (PNGs). However, Java's .json models are often formatted differently than Bedrock’s .geo.json models. You’ll likely need a tool like Blockbench to import the Java model and export it specifically for Bedrock.
You need to write (logic) and Resource Pack (visuals). Since you have a Java mod, use a converter tool for the boring stuff: how+to+convert+jar+to+mcaddon+verified
A Java .jar file contains compiled Java bytecode. Bedrock cannot read Java bytecode. You cannot convert the logic automatically. You can often reuse the textures (PNGs)
Bedrock needs a manifest.json in BOTH folders. Without this, your mod is a ghost. your mod is a ghost.