It does work in a similar way to English, with sequence of tenses, but only under certain circumstances. If the underlying sentence begins with the verb "bod" in the present tense (including the perfect tense with "wedi"), or with any verb in the preterite tense, or with some element other than a verb, then it works in a completely different way. If the underlying sentence of the indirect clause begins with a verb that isn't the present tense of "bod", then it is simply linked to the main clause with "y" (which is often not heard in speech), and the tense changes more or less as in English (i.e. future > conditional), e.g. "Bydda i'n dŵad adre" --> "Dywedodd o y byddai'n dŵad adre"). If the verb is in the preterite tense, it can work like that too, or else another construction can be used in which the verb is changed into the verbal noun and the subject becomes the object of the preposition "i", which introduces the clause, e.g. "Mi fwytodd o frechdan" --> "Dw wedi clywed iddo fwyta brechdan". If the underlying sentence of the indirect clause begins with anything other than a verb, then it is linked to the main clause with "mai" (which can be "na" or "taw" dialectally): "Pysgotwr ydy fy nhad i" --> "Mae o'n dweud mai pysgotwr ydy ei dad o". As you've probably realised, it's extremely common for a Welsh sentence to begin with the present tense of "bod" ("dw", "wyt", "mae"...), and in this case the verb of the indirect clause changes to a possessed form of "bod" with the subject as possessor, e.g. "mae o'n mynd allan" --> "dywedodd o (ei) fod o'n mynd allan"; "dw i wedi llyncu pryf" --> "dw i'n meddwl (fy) mod i wedi llyncu pryf" (the possessive adjective is often dropped in speech but its mutation remains). As you can see, it's quite complicated. If you need any further elucidation, don't hesitate to ask.