Because present participles end in -ing in English, you must be very careful that you aren't confusing them for gerunds and vice versa.
In English, we use present participles to make the progressive present tense. This isn't done in Sindarin. If you find yourself translating "[to be] _participle_," you need the present tense verb conjugation.
For the A-verb, take the A off the root and add -ol.
glavra- babble → glavrol babbling
For the I-verb, add -el onto the root.
cab- leap → cabel leaping
For I-verbs ending in -ir, add -iel onto the root.
tir- guard → tiriel guarding
This adjective describes something that is being done while people are talking about it. It can't be made plural.
Suilannen i n�r bedel. - I greeted the talking man.
You can also use present participles like a gerund, except that they indicate an action that is happening simultaneously with the main action. Both actions must have the same subject.
Pedel oh auth padrassen. - (while) Talking about war I walked.
Madel lembas padrassen. - (while) Eating lembas I walked.
Padrassen lastol i veldis n�n i ebent oh auth. - I walked (while) hearing my friend who spoke about war.