There is no future tense in Gnomish or Early Noldorin, perhaps because the Welsh present tense can also be used to describe the future: strictly speaking the Welsh “present tense” is really “non-past”, just like the English simple present. The first mention of a distinct future form is in Quendian & Common Eldarin Verbal Structure (EVS1) from the late 1940s:
Sindarin (and it’s conceptual precursors) have two major classes of verbs: basic verbs (based on an unadorned primitive verbal root) and derived verbs (produced with some kind of verbal suffix). In the literature, these two classes are sometimes called i-stem verbs and a-stem verbs after their present tense forms, which frequently have i or a respectively. For example, this terminology appears in David Salo’s book, Gateway to Sindarin (GS/111), though I am not certain he first coined these terms.